1986 Honda TRX 250R proof mixed parts don't make power
So a few months ago I was approached by a complete stranger to build him a nice TRX 250R. At first I was a bit hesitant at this point I am a bit tired of ATV's and building them from ground up. But me being who I am and owner no being at all mechanically inclined I told him ok but I was going to need parts and asked what he specifically wanted. Well owner ended up buying 3 total bikes to build his dream bike. So first frame he brought was cracked, now junk bought a nice bulk powedercoated frame with title. Next motor was fried and not only fried but cylinder was on second to last bore so paperweight now, crank was ok but wanted and got a tighter OEM crank from a spare bike he bought that look like crap but motor was in good condition. I sent many parts to chrome, polish , or powder coat and there was allot based on owners color of bike wanted.
So owner did not want to use race gas and super unleaded so I could not lower compression and therefore I ended up using a stock uncut head with an OEM TRX 250R head gasket after I split cases to install new OEM Honda bearing and new seals. I ended using another cylinder from a bike he bought was not happy with it it was on 3rd bore but was an 86 cylinder (not a bit fan of stock 85-86 cylinders). So carb I was givin to use was a 39mm air Stryker which I knew was not going to work and a bBills pipe I sent to polisher to make nice again. I used a set of new VForce 3 reeds which I knew would be good or help and used stock gearing both front and back!
After everything was done and assembled did usual break in and sent bike to Jerry Hall in Glendale Az to do tuning 3/20/19.
3 weeks later Jerry called bike was ready drove to Glendale picked up and was not surprised how little power was made because of mixed parts that were used! But jetting Jerry set for 39mm air Stryker are 1.75 main jet, 48 pilot jet. 1.5 turns air screw and replaced needle to DEF-4 needle foam UNI filter with no lid on 89 pump gas. Really quick on 39mm air Stryker, owner purchased carb on eBay and was not aware until Jerry saw carb and asked me if carb was bought on eBay at time didn't know but called owner and confirmed it was bought on eBay. But Jerry said eBay 39mm air strykers are no good they come with generic needle, pilot jet and main jet and more important on att three they don't have numbers or sizes so you don't know what you are installing on your bike so be careful.
But was not surprised at power for what Jerry got out was Max power 36.96 and Max Torque 27.78 which is low in my opinion on a fresh build I have done. I also took my nephews 88 TRX 250R with an 85 Honda ATC motor stock pipe with answer silencer stock reeds with an OEM 1985 Honda ATC 250R head gasket with stock carb. Main jet 158 UNI air filter no air box lid Max power 34.63 Max Torque 26.26> I took nephews bike because he needed tune but because wanted comparison as well between almost stock to mixed and unmatched parts.
Well I now have data to prove bigger not always better and mistakes I will never do or throw money in garbage.
But also year before I sent Jerry my junkyard 86 @50R that was assembled from parts I had in tote boxes and parts laying around in garage. I used on my parts bike stock non ported 2nd overbore 88-89 cylinder, 88-89 Curtis Sparks engraved cylinder head uncut, 1985 OEM Honda ATC 250R head gasket, VForce 3 reeds, 38MM PJ carb, FMF SST Pipe, Jerry Hall Dyno tuned as well 12/5/2018 Max Power 40.66, Max Torque 29.59.
So my point in all this is with all data acquired bigger is always not better and Jerrys knowledge 88-89 cylinders always better they just flow more, and adding compression with a big carb always beneficial and using correct pipe at your desired RPM range is also crucial!
Jerry said that that Bills pipe would be perfect on big bore with appropriate bigger core silencer. But didn't think with that 86 cylinder I used adding higher compression would of made much difference!
Thanks for reading but Blk bike is clients bike with 36.96 Hp and Blue bike is bike that made 40.66
Last edited by aztecgwynn; 09-28-2019 at 03:28 PM.
Good write up Mike; takes work to get the most out of any engine, even 250R's.
Carlos thank you, not that I am an expert as you are, and I never will but I am still learning every time I get into one of these 250R's.
Listening to you and Jerry and taking in as much info has helped me tremendously building these motors. To this day I just eat up when Jerry speaks. Sometimes it is hard to understand him because he is an educated engineer and at times I don't know his lingo. But I come back to him when he is done and I ask him questions to clarify!!!!!!