85r motor swap question

[trikeguy2014]

So I wanted to give my 85r it's time to shine, I just finished up a motor swap taking my 86 trx 250r motor carb setup and putting it on my 85 atc 250r. They both ran good before the swapping but my trx is a really fresh motor from BDT racing. The 86 trx had a 38mm keihin and my 85r is still on its stock round slide. Both have full fmf systems. When I got my trike finished I took it for its test ride and something just isn't quite right. It's idling kinda high and stuttering showing a lean symptoms (I believe). I just wanted to make sure the electronics are not different causing my problem before I begin attempting any jetting. I did a short ride so I would not do any damage if the electronics are the problem. And everything plug up the same so I did no custom anything.
Any help would be great because if I need to do a swap back before trike fest comes as it's fast approaching and I don't want to leave number 27 at home!

And no I haven't put my trx back with the 85 motor I wanted to see how it went before it got put back together

[Eric250R]

Intake boot in good shape ? Any cracks that could cause a small air leak ?

[BOB MARLIN]

I'm running a BDT trx motor in my 85R. There was no change in the electronics. I think you have something else going on.

[yaegerb]

Stuttering where? On idle? If not, what throttle position? Need specifics on what's exactly going on.

[trikeguy2014]

Yeah intake boots everything is in good shape, I'll give it a good once over again and make sure. Could it just be running a tad lean from being a different pipe and intake boot etc?

[yaegerb]

It could be running lean for multiple reasons. Intake leak, failed seals, wrong jets. I would spray carb cleaner over intake joints while it's running to see if it dies. The I would do a pressure test. What jets in carb? Any port work, head work? Different reeds?

[trikeguy2014]

High idle some stuttering from about half on to full throttle... Engine ran perfect when it was in my trx, I just pulled it out and did the swap. I just wanted to be sure it wasn't anything electrically different that would cause it the problem

[trikeguy2014]

Reed assembly and carb throttle and cable everything came off straight from my trx.

[yaegerb]

Have you checked for intake leaks and/or pressure tested the motor?

[trikeguy2014]

I'll spray some carb cleaner around all the intake joints and see if it dies or not.

[yaegerb]

So essentially you put an 86 trx motor and 38 mm carb on your 85 250r? it was running perfect in the trx? What airbox were you using on the trx vs now on the ATC?

[trikeguy2014]

Yeah that's all I did, both setups were on air boxes with lids and full fmf systems. The engine carb reeds was all from my trx

[yaegerb]

All things being equal; if it was running good before it should be running good now. Double check intake leaks, and electrical comnections.

[trikeguy2014]

Still no luck looks like this wknd I'll be switching back to my 85 motor, I still believe it's something electrically, jetting can't be that far off. I'm having eratic idle, doesn't die but sometimes idles high sometimes it's fine. also it just stutters a lean sound and just doesn't have much power. I don't know what else to do.

[atc300r]

Try putting the trx coil on the atc.

[RIDE-RED 250r]

Your '86 TRX CDI should not plug into your '85 ATC harness. So I am guessing you are running your ATC CDI?? Are you running the coil from your TRX as well or are you running the ATC CDI?

What you are describing sure sounds like a fuel mixture issue to me, whether it be a jetting issue you need to dial in or as suggested, you may have an air leak somewhere that you haven't found yet.

You shouldn't have any issues plugging on your 86 TRX engine harness to your '85 ATC chassis harness, or running your '85 coil. If your '85 engine ran fine too, then I would say electrical is probably not your problem.

The ATC pipes are different than the TRX pipes and may require different jetting specs to dial in right. But having said that, I would expect the differences to somewhat small.

[trikeguy2014]

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some pictures for you guys, I just unplugged the 4 wires coming from the stator. the plugs and wire colors were the same from both motors like you guys said. so maybe it is just my jetting???

[yaegerb]

The only way your jetting will be off is from either the airbox, pipe, or you have an airleak some where. This isn't rocket science. If it worked on your trx, the only variables that changed was the length of your expansion chamber, your airbox (which you said was an identical setup), an airleak has now developed or your electrical system has an issue.

What did the ATC run like before you pulled the motor?

[fieldy]

What does the motor do when it idles and you use the choke some? Does that change the idle speed?

[trikeguy2014]

Yeah your right it shouldn't be, both ran boxes with lids shape is obviously slightly different. Pipes shape is quite a bit different but both are fmf. I'll do some more looking this weekend, work is always in the way, and try to get this figured out, if not I guess I'll swap back motors for now.

Thanks for all information, any more just post it, any suggestions are better than none

Atc ran good and trx ran good (when something isn't broke don't fix it) ("bordom I guess")

[trikeguy2014]

Haven't tried choke yet, never thought about seeing if it changed anything. I'll give it a try and see


Also this hasn't been brought up but I use same gas and oil in both so that's not it if someone is thinking it, klotz r50 40:1

[fieldy]

Just a possibility that you have gotten a piece of dirt in the carb. I would try to blow air through the carb or use a carb cleaner with a straw first. I had this happen before. Then if it still revs, i wouldnt mess around, do a pressure test. Maybe the intake leaks since you may have put some pressure on it swapping things. If it tries to idle really high pull the choke out so it stops running. Check throttle cable too.

[trikeguy2014]

I'm going to eliminate jetting and intake off my list. I sprayed starter fluid all over the intake boots and it didn't effect anything at its idle at all. I went up on main jet in several steps. First size or to helped slightly but not even close to what it should be. It did seem to help idle as it idles normal, not sure why, but it still will not hit power band very hard and just stutters at half throttle on.

[yaegerb]

I'm going to eliminate jetting and intake off my list. I sprayed starter fluid all over the intake boots and it didn't effect anything at its idle at all. I went up on main jet in several steps. First size or to helped slightly but not even close to what it should be. It did seem to help idle as it idles normal, not sure why, but it still will not hit power band very hard and just stutters at half throttle on.

Main jet increase will not help your idle circuit. So either you imagined your idle was rough or something else has changed since you dropped it in. Above you mention that both pipes are FMF which doesn't matter. The length of your expansion chamber and carburetor jetting go hand in hand. So if it's not an airleak, it's either jetting because of the different pipe or an electrical issue (but you said the ATC motor ran fine).

[trikeguy2014]

All time let down today, I tried jetting up thought it was lean like I said that didn't help. So today I decided to put the main jet from trx back in it. Still terrible so I pulled air box lid off. Great! Ran clean tons of power a light blue smoke everything seemed great. Then it started acting really weird started to try and die so I killed it. Now it will hardly kick over (I didn't try hard but defiantly not right) my perfect running trx 250r that had about 10 hours since it was gone through powder coated and chromed is done. Explain that???? Guess it's time to get that 85 motor back in

[RIDE-RED 250r]

Sorry to hear that. The only person who can explain that is you, and the only way you will be able to explain it is to start the autopsy on the engine.

Get your '85 mill back in, go to TF and enjoy yourself. Once you get back, start digging into that engine. Please post up what you find, pics would be great too. I myself am curious to know what happened.

[trikeguy2014]

That's the plan... I'll definatly post back when I get some answers, I don't even want to see inside that motor now, maybe ripping it up at trike fest will get me in the mood to break the engine down and see what went on

[fieldy]

If you could look at the spark plug first then take it and have the 250 pressure tested before disassembly. I am also interested in why all the sudden you had trouble and how many hard hours were on the newly rebuilt TRX motor.
To remove an airbox lid and garage/yard run it and a overheats/semi-sieze? Thats....yeah let us know. Maybe those guys who built it will work with you on the repair since you are their customer.
If the pressure test is good, then its gonna get interesting! Have a good trikefest!

[trikeguy2014]

I put a few hours on my trx just taking it real easy, probably more than I needed, but I wanted to take the extra precaution on it. I had 2 trips to haspin, several rides around the house and farm on the trx after the break in, I'm guessing around 8 hours of actual hard riding on it. It ran great, no leaks no problems out of it till the swap. Like I said I'll post back after it gets pulled apart. I did get swapped back and we should be good to go for trikefest, least I hope

[trikeguy2014]

Also spark plug was good color, about perfect when pulled it after it cooled down. The next day I was able to roll it over by hand, so hopefully I got it shut down without extensive damage.

[yaegerb]

I put a few hours on my trx just taking it real easy, probably more than I needed, but I wanted to take the extra precaution on it. I had 2 trips to haspin, several rides around the house and farm on the trx after the break in, I'm guessing around 8 hours of actual hard riding on it. It ran great, no leaks no problems out of it till the swap. Like I said I'll post back after it gets pulled apart. I did get swapped back and we should be good to go for trikefest, least I hope

So the trx won't kick over now? This is a motor from BDT?? What was done to this motor? Holy shite man, issues galore. How does a trx motor with only 8 hours crap out that fast. Get your money back or you didn't break it in properly.....something isn't adding up.

[trikeguy2014]

It started to seize up, I'll post back when I find out more, I don't think it was there fault, I think I know what happend but I want to be sure before I jump to conclusions. It will be after trikefest sometime.

[RIDE-RED 250r]

Every good builder stands behind their work if the failure was a shortcoming or mistake on their end. Not saying anything bad about BDT specifically here, but mistakes do happen and they can happen with anyone.

I still cannot think of a single reason swapping the mill into your ATC would be detrimental other than some oversight on your part and it seems as though you covered your bases. At this point I am thinking it is an incredible coincidence that something let go after the swap.