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Discussion Starter · #1 ·
Hello everyone, I’m new to this forum and was hoping to get some tuning advice on my drag quad. This is my first 250R and it has been quite a learning experience so far. Here’s a little background real quick. I bought the quad earlier this spring with the intention of drag racing it this season, however after getting it home it became nothing but problems. Bought brand new 39 pwk carb and vforce 3’s for it and tried several different jetting combos and still had issues. Long story short I recently figured out that I had been running the wrong spark plug type in it the whole time. Guy I bought it from had a NGK bpr7hs in it and said that is what he usually runs in it. I later figured out it only threads halfway down into the head when it’s supposed to have either a br8es or br9es. Really felt like an idiot because it took me way too long to figure this out. Should’ve known better to trust this guys word. Anyway, now that I finally have the proper spark plug and can actually tune it properly, I have been working on getting it dialed in. The current bike setup is as follows
1988 trx250r
Ftz race ported 1986 style cylinder .010” oversized bore with cylinder spacer plate
Wiseco prolite piston
Vforce3 reeds
Ftz in frame wide pipe
Pro design 18cc cool head running about 150 psi per the last compression test
39 mil keihin pwk
48 pilot
162 main
Air screw 1.5 turns out
Needle on 3rd clip (middle)
I run Sunoco 110 (cam 2) with klotz super techniplate at 32:1

In the pics below, the first two images are the plug threads with br9es on the right and br8es on the left. The pics of the porcelain are vice versa. I have been doing a bunch of research on plugs lately trying to gain a good understanding of them. From what I have read, the ground strap will show a blue band at different points along the strap depending on heat generated in the cylinder in relation to spark plug heat range. This is how you tell if you are in the correct heat range of plugs and also if your timing is too far advanced or retarded. With the blue band ideally being somewhere in the middle of the ground strap close to the curve. Too close to the electrode and too cold and too close to the threads or not showing at all, then too hot. Looking at the br8es (Left) ground strap I can’t really see any distinct blue band, unless I’m not looking at it right. On the br9es, it looks like the blue band is visible where the ground strap is welded to the threads. Am I looking at this right or am I completely off? If this is right, then the br8es is way too hot and the br9es is better, but still may be too hot?
Looking at the porcelain, it appears that the br8es (right) has a yellow glazed tip, then a dark midsection, and a light grey upper ring. From what I have read the yellow glazed tip is from rapid heating of the deposits on the plug before they are able to burn off so it is just melted into the porcelain. This yellow glazed tip can indicate that the plug is getting too hot. After this I ran the br9es plug and did a chop. It looks like the tip is still showing some yellow glazing, but not as much. Still a dark midsection, but the upper ring is mostly white. Is this still too hot of a plug or is this in the right range? I have read that the tip of the plug shows your idle/low speed jetting, the mid section shows you’re midrange, and the top ring shows your WOT. Is this correct? I should mention that I did not do a “proper plug chop” on these two plugs. What I did was do a few pulls, then let the bike sit for 30 minutes or so to cool down a bit then do a few more pulls on the same plug then pull it immediately after. I did this for both plugs. I did not shut the motor off after hitting WOT like in a “proper” plug chop. I also ran at low rpm’s in a tall gear in between pulls to help cool the motor off in between runs. This very well may be why both plugs have dark midsections and glazed tips due to the carbon buildup from riding at low rpm then getting torched from the WOT pulls. Am I on the right track with my train of thought or am I completely wrong and need to approach this differently? Am I running my jetting too rich? I’m hesitant to lean it out much more because it smokes very little out the exhaust already. I’ve actually been considering upping my oil mixing ratio to 28:1. From what I understand, I would need even richer jetting then to compensate for the extra oil taking up space that the gas once occupied in order to run the proper air/fuel ratio. Any experienced advice would be extremely helpful with all of this. Somebody please school me haha. I apologize for the long post, but like I said, this is my first 250R and I really want to get this thing dialed in. Thanks for your time
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Discussion Starter · #2 ·
Hello everyone, I’m new to this forum and was hoping to get some tuning advice on my drag quad. This is my first 250R and it has been quite a learning experience so far. Here’s a little background real quick. I bought the quad earlier this spring with the intention of drag racing it this season, however after getting it home it became nothing but problems. Bought brand new 39 pwk carb and vforce 3’s for it and tried several different jetting combos and still had issues. Long story short I recently figured out that I had been running the wrong spark plug type in it the whole time. Guy I bought it from had a NGK bpr7hs in it and said that is what he usually runs in it. I later figured out it only threads halfway down into the head when it’s supposed to have either a br8es or br9es. Really felt like an idiot because it took me way too long to figure this out. Should’ve known better to trust this guys word. Anyway, now that I finally have the proper spark plug and can actually tune it properly, I have been working on getting it dialed in. The current bike setup is as follows
1988 trx250r
Ftz race ported 1986 style cylinder .010” oversized bore with cylinder spacer plate
Wiseco prolite piston
Vforce3 reeds
Ftz in frame wide pipe
Pro design 18cc cool head running about 150 psi per the last compression test
39 mil keihin pwk
48 pilot
162 main
Air screw 1.5 turns out
Needle on 3rd clip (middle)
I run Sunoco 110 (cam 2) with klotz super techniplate at 32:1

In the pics below, the first two images are the plug threads with br9es on the right and br8es on the left. The pics of the porcelain are vice versa. I have been doing a bunch of research on plugs lately trying to gain a good understanding of them. From what I have read, the ground strap will show a blue band at different points along the strap depending on heat generated in the cylinder in relation to spark plug heat range. This is how you tell if you are in the correct heat range of plugs and also if your timing is too far advanced or retarded. With the blue band ideally being somewhere in the middle of the ground strap close to the curve. Too close to the electrode and too cold and too close to the threads or not showing at all, then too hot. Looking at the br8es (Left) ground strap I can’t really see any distinct blue band, unless I’m not looking at it right. On the br9es, it looks like the blue band is visible where the ground strap is welded to the threads. Am I looking at this right or am I completely off? If this is right, then the br8es is way too hot and the br9es is better, but still may be too hot?
Looking at the porcelain, it appears that the br8es (right) has a yellow glazed tip, then a dark midsection, and a light grey upper ring. From what I have read the yellow glazed tip is from rapid heating of the deposits on the plug before they are able to burn off so it is just melted into the porcelain. This yellow glazed tip can indicate that the plug is getting too hot. After this I ran the br9es plug and did a chop. It looks like the tip is still showing some yellow glazing, but not as much. Still a dark midsection, but the upper ring is mostly white. Is this still too hot of a plug or is this in the right range? I have read that the tip of the plug shows your idle/low speed jetting, the mid section shows you’re midrange, and the top ring shows your WOT. Is this correct? I should mention that I did not do a “proper plug chop” on these two plugs. What I did was do a few pulls, then let the bike sit for 30 minutes or so to cool down a bit then do a few more pulls on the same plug then pull it immediately after. I did this for both plugs. I did not shut the motor off after hitting WOT like in a “proper” plug chop. I also ran at low rpm’s in a tall gear in between pulls to help cool the motor off in between runs. This very well may be why both plugs have dark midsections and glazed tips due to the carbon buildup from riding at low rpm then getting torched from the WOT pulls. Am I on the right track with my train of thought or am I completely wrong and need to approach this differently? Am I running my jetting too rich? I’m hesitant to lean it out much more because it smokes very little out the exhaust already. I’ve actually been considering upping my oil mixing ratio to 28:1. From what I understand, I would need even richer jetting then to compensate for the extra oil taking up space that the gas once occupied in order to run the proper air/fuel ratio. Any experienced advice would be extremely helpful with all of this. Somebody please school me haha. I apologize for the long post, but like I said, this is my first 250R and I really want to get this thing dialed in. Thanks for your time
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I should also add that it has a pvl ignition. I do not know the timing setting as it was already set by the guy I bought it from, but I will be ordering a dial indicator ASAP to figure that out. Also if I remember right I could have sworn that the compression test I did shortly after I bought it in April, I was able to get it up to about 170 psi after several minutes of kicking. I did one today and the gauge quit climbing around 150 psi. I feel like it shouldn’t take this many kicks with the carb slide wide open to get a good compression reading and also that an 18cc cool head should have much higher compression than 150? Could this indicate that the motor is going bad already? The guy I bought it from had the motor apart and literally put it together the day before he sold it to me. As I said earlier, I was not able to get the motor to run right for the longest time, therefore I wasn’t able to run it through proper break in heat cycles. To be honest I didn’t really know just a few months ago what I know now and probably wouldn’t have run it through heat cycles anyway. Would this cause premature wear of piston rings, cylinder walls, etc, to the point of losing compression? Or could it be something else possibly causing this?
 

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The first thing you should do is figure out why your engine has only 150 psi, especially if the previous owner just rebuilt the top end. A properly assembled healthy stock engine with a stock TRX headgaket will have around 180 psi which is still under the level needed for running the race gas your currently using. A leak down would also be a good idea just to make sure the engine's sealed up. As far as jetting there's tons of info on this site & on trx250r.org that can help get you in the ballpark.... For reference both my 86's have stock 85-86 heads & 85-86 atc head gaskets, both have 205psi cranking compression. One engine has a stock 88 cylinder at 66.75mm & hotrods long rod crank & the other one has a clean up ported 86 cylinder at 67.5mm & hotrods short rod crank.
 

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Discussion Starter · #4 ·
I should also add that it has a pvl ignition. I do not know the timing setting as it was already set by the guy I bought it from, but I will be ordering a dial indicator ASAP to figure that out. Also if I remember right I could have sworn that the compression test I did shortly after I bought it in April, I was able to get it up to about 170 psi after several minutes of kicking. I did one today and the gauge quit climbing around 150 psi. I feel like it shouldn’t take this many kicks with the carb slide wide open to get a good compression reading and also that an 18cc cool head should have much higher compression than 150? Could this indicate that the motor is going bad already? The guy I bought it from had the motor apart and literally put it together the day before he sold it to me. As I said earlier, I was not able to get the motor to run right for the longest time, therefore I wasn’t able to run it through proper break in heat cycles. To be honest I didn’t really know just a few months ago what I know now and probably wouldn’t have run it through heat cycles anyway. Would this cause premature wear of piston rings, cylinder walls, etc, to the point of losing compression? Or could it be something else possibly causing this?
Correction: I verified with the guy I bought it from and he DID NOT have the motor torn apart before he sold it to me. He was ABOUT TO tear it apart to put stock trans gears in it but never actually did. The piston and cylinder is just really old back from when FTZ originally built it. So no need for break in heat cycles. The piston and rings are most likely just worn out from age possibly causing compression loss?
 

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Hello everyone, I’m new to this forum and was hoping to get some tuning advice on my drag quad. This is my first 250R and it has been quite a learning experience so far. Here’s a little background real quick. I bought the quad earlier this spring with the intention of drag racing it this season, however after getting it home it became nothing but problems. Bought brand new 39 pwk carb and vforce 3’s for it and tried several different jetting combos and still had issues. Long story short I recently figured out that I had been running the wrong spark plug type in it the whole time. Guy I bought it from had a NGK bpr7hs in it and said that is what he usually runs in it. I later figured out it only threads halfway down into the head when it’s supposed to have either a br8es or br9es. Really felt like an idiot because it took me way too long to figure this out. Should’ve known better to trust this guys word. Anyway, now that I finally have the proper spark plug and can actually tune it properly, I have been working on getting it dialed in. The current bike setup is as follows
1988 trx250r
Ftz race ported 1986 style cylinder .010” oversized bore with cylinder spacer plate
Wiseco prolite piston
Vforce3 reeds
Ftz in frame wide pipe
Pro design 18cc cool head running about 150 psi per the last compression test
39 mil keihin pwk
48 pilot
162 main
Air screw 1.5 turns out
Needle on 3rd clip (middle)
I run Sunoco 110 (cam 2) with klotz super techniplate at 32:1

In the pics below, the first two images are the plug threads with br9es on the right and br8es on the left. The pics of the porcelain are vice versa. I have been doing a bunch of research on plugs lately trying to gain a good understanding of them. From what I have read, the ground strap will show a blue band at different points along the strap depending on heat generated in the cylinder in relation to spark plug heat range. This is how you tell if you are in the correct heat range of plugs and also if your timing is too far advanced or retarded. With the blue band ideally being somewhere in the middle of the ground strap close to the curve. Too close to the electrode and too cold and too close to the threads or not showing at all, then too hot. Looking at the br8es (Left) ground strap I can’t really see any distinct blue band, unless I’m not looking at it right. On the br9es, it looks like the blue band is visible where the ground strap is welded to the threads. Am I looking at this right or am I completely off? If this is right, then the br8es is way too hot and the br9es is better, but still may be too hot?
Looking at the porcelain, it appears that the br8es (right) has a yellow glazed tip, then a dark midsection, and a light grey upper ring. From what I have read the yellow glazed tip is from rapid heating of the deposits on the plug before they are able to burn off so it is just melted into the porcelain. This yellow glazed tip can indicate that the plug is getting too hot. After this I ran the br9es plug and did a chop. It looks like the tip is still showing some yellow glazing, but not as much. Still a dark midsection, but the upper ring is mostly white. Is this still too hot of a plug or is this in the right range? I have read that the tip of the plug shows your idle/low speed jetting, the mid section shows you’re midrange, and the top ring shows your WOT. Is this correct? I should mention that I did not do a “proper plug chop” on these two plugs. What I did was do a few pulls, then let the bike sit for 30 minutes or so to cool down a bit then do a few more pulls on the same plug then pull it immediately after. I did this for both plugs. I did not shut the motor off after hitting WOT like in a “proper” plug chop. I also ran at low rpm’s in a tall gear in between pulls to help cool the motor off in between runs. This very well may be why both plugs have dark midsections and glazed tips due to the carbon buildup from riding at low rpm then getting torched from the WOT pulls. Am I on the right track with my train of thought or am I completely wrong and need to approach this differently? Am I running my jetting too rich? I’m hesitant to lean it out much more because it smokes very little out the exhaust already. I’ve actually been considering upping my oil mixing ratio to 28:1. From what I understand, I would need even richer jetting then to compensate for the extra oil taking up space that the gas once occupied in order to run the proper air/fuel ratio. Any experienced advice would be extremely helpful with all of this. Somebody please school me haha. I apologize for the long post, but like I said, this is my first 250R and I really want to get this thing dialed in. Thanks for your time
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I don't understand, what's the issue with the plugs, one threading in and not the other since they're exactly the same threadwise?...also, for a drag bike, most of your equipment including that tiny carb is all wrong, you'd think you'd be running a huge Lectron...with what u have, I don't think you'll be developing the needed HP yo be anywhere near the top...also, when you're talking about the "issues" you're encountering, what are the issues???..."don't just say "I'm having issues" and expect everyone to pinpoint the resolution to your problems...be very descriptive...
 

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Discussion Starter · #6 ·
The “issues” I was talking about was just me giving some background of what’s happened since I’ve bought the bike. Those issues have since been resolved. Which is why I didn’t go into detail about any of them. I do not expect anyone to “pinpoint the resolution to my problems” if I just give a generic description. The wrong spark plug with it not threading all the way down was one of those issues and it was taken care of. Which is neither of the spark plugs pictured, because like you said they are both the same length. I guess the way I worded it may have caused some confusion. My main reason for posting is looking for opinions on reading the two spark plugs pictured. They are the same plugs pictured from four different views to give a good all around picture. And also possible jetting recommendations based on the spark plug pics.
Also, do you have any drag racing experience? Besides my “tiny carb”, why is my “equipment all wrong”?
 
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