Motor swap mystery
 

OK so thanks for fielding all my wacky questions, BUT

The swap is done (98 motor out, 05 motor in). I fired it up today and it showed the EXACT SAME PROBLEMS AS THE OLD MOTOR!!!!!!!.

Only runs on choke, white smoke out the rear cylinder, etc. No way could both motors have the same issues, so I must look elsewhere. Maybe a carb float is stuck? I dont recall seeing this before but its weird.

If anyone has seen or heard anything like it let me know. I havent looke much but both spark plugs are firing visually strongly.

are you using the same carbs?

Could be that the rear carb is dumping too much fuel into the rear cyl. I have seen excessive fuel cause white smoke in cars(stuck injector). If you have the old motor still, I'd pull the head off and see if you find anything obvious. Look for signs that the fire ring of the head gasket was compromised. Sounds to me like you have a candidate for a bitchen engine build now, as in a good usable core.

How does it run? It could also be that the carb has a crack in one of the cooling passages, and is allowing coolant in that way. Get some needle nose vice grips if you have them, or regular ones if you don't, and pinch off the coolant hose to the carb. DON'T GO TO TIGHT! If you do, you could damage the hose. You want just enough to stop the flow of coolant to the carbs.

That sounds reasonable. For years I had the coolant lines to the carbs clamped to prevent flow. Recently I unclamped one ( the rear I think). This has been frustating since racing keeps taking me out of town so days go by that I cant dig into it.

Oh yeah, same carbs, same everything, new motor.

Probably be a good idea to test new engine leakdown and compression. Probably a good time to check / adjust valves. Then tinker with carbs. Just my 2 sense.

That a good idea, once he gets it running better. If he can't get it warmed up necause it puking smoke, the compression and leak down tests will not be accurate. Those are supposed to be done on an engine at operating temp.

my thinking could be too simple but.... seems to me if everything changed except the carbs, and the problem persists.... then its gotta be the carbs.

If it's fuel, the plug and piston should be covered in black soot.

If it's coolant they will be way too clean.

Same fuel?

Depends on how much fuel. Remember, fuel is a solvent. So if it's putting so much fuel in the cyl. that it's blowing white smoke, the cyl. will look the same as a coolant steamed cyl. I had to find that one out the hard way. I was a young auto tech, and did a cyl head gasket under warranty because a car was belching white smoke and was down a cylinder. Pulled the head off without a proper diagnosis and couldn't find anything obvious(I was frustrated because of what car it was, and assumed it was a head gasket because of how much a bitch it was going to be). Replaced the head gasket and the problem was still there. So I did a proper diagnosis and found out that one of the injectors was stuck open. Luckily it was under warranty, so the repair was covered. Had it been on the customer for the repair, I would have done a cylinder head gasket on a PT Cruiser Turbo for free. Not exactly the easiest car to do a head gasket one.

+1. New engine, same problem. I highly doubt that the new engine has the exact same problem. Block off the coolant passages, rinse, repeat.

I see your point, and it's definatly valid, if it was both cylinders. But, it's only 1 cylinder, so I doubt it's the fuel.

I had an issue with my SH running like sh@# after sitting for a while... it ran like as$ and at the same time acting as if it was running out of gas and getting too much gas..

turned out to be the float pin was sticking and I was able to free it up and scrape off the crap and put it back together...

ran fine after that, dont know if this helps but it was my experience

If it will only run on choke that is saying something about the running conditions of the bike/jetting.

If it was previously running properly and NO jetting changes were made, you may have a clogged main jet or emulsion tube. If it is not one of those then you should flush out the fuel inlets and see where the fuel is coming out. I would recommend pulling the slides out as the diaphragms are somewhat fragile.

If one of your chokes nuts is cracked and the plunger is not closing the enrichment circuit all the way, that may be why it isn't running properly as well. Mine is broken off completely and I have to run on almost full choke because the difference between the cylinders is enough to change whether it will run or not. If it's not cracked, double check to make sure that the seal on the end of the brass plunger is okay as well because that could be broken as well.

For other "duh" moments, check carb boots for leaks, double check plugs and coils. Not likely the problem, but once you've removed all other options, what's left is the solution :)

and just as a question that could help you later on down the line, do you have another bike with a fuel pump that you could use to pressure test your carbs?

Is it like this?

02-25-11 Bike Wars episode 2 WTF! - YouTube

Yes geek it resembled that condition alot except mine runs at idle but dies at throttle input. I disassembled and cleaned the carbs to get to this point. BTW you didnt have to dismantle the throttle at the grip, just remove the 2 small screws holding the cables onto the carbs.

im wondering,and this is for giggles,but,is it possible that maybe the petcock is failed and the diaphragm is split just a little where there is fuel returning to the head thru the vacuum port.
geek had that same problem,but his was more entertaining lol.his was 1 in a million.dont know how it was running.
but that could cause smoke and to run crappy.just a thought.

Yah on my bike my petcock was not engaging because it was loose. So they might be similar problems. Even if your choke is working I am willing to bet you have a fuel issue.

Yes, a fuel issue, did you replace or repair the petcock? I have the same smoke as on one of your videos. Saige, what was the resolution?

I had bad luck with a rebuild kit. This OEM part number has all the gaskets and such that can go bad, save one spring (which really can't go bad):

16953-ML0-034

I used it and it solved some petcock issues that I had...

we didnt want to wait for a rebuild kit,i had a extra petcock and gasket,so i went over and help him change it and problem gone,luckily the petcock was a good one.
geeks had a minute tear in the diaphragm and that caused a leak,but like i said,his was one in a million,the vacuum was on the wrong nipple (geek,for the love of god,try not to laugh) and it still ran for months and months.so once it was changed,no fuel was going into the head anymore and it ran stronger than before.
i would say,try to source a good petcock or get a full good rebuild kit,its a cheap start.hopefully,that is the problem or will lead you to it.
one question,is smoke coming out of both cans or just one.if just one,it should be your left can.

OK but when I apply vacuum to the petcock it gushes fuel out the 2 feeds, no leaks so I dont think I have that issue, right?

Nah it doesn't sound like it. FWIW mine still functioned when it wasn't working correctly (as in gushed out both sides). But other than that my symptoms were all completely different from yours. And it sounds like Geek was sucking fuel into his rear cylinder through the vacuum line, which is a one in a million shot!

I'm kinda curious about the smoking exhaust now... is it coming out of both pipes?

Are your carb slides seated correctly? If you pull them back, do they return kinda slowly or snap back quickly? They should return slowly...

I cleaned and reassembled the carbs and they both seem to slowly slide shut so I think the diaphragms are sealing. Cant open the throttle still tho

The gas was coming back thru the vacuum into the head,but some gas came out the mid pipe.
My guess is choke related or maybe something fell in and is clogging the throttle body.

Do you have oil in the airbox? Sometimes high oil level or excessive crankcase pressure can force oil into air box. Seen excessive blow by cause the pressure or even a carb leaking fuel into cylinder then leaking past rings causing higher oil level and excess pressure. Carb coolant leak as mentioned above sounds plausable as well.

OK guys. I am including this only to save others the same fate. It was all due to bad gas, maybe a tankful of diesel somewhere near Binghampton on my trip home.

That is why the new motor acted the same. I finally broke down & swapped the tank from my other vtr and it is running better. Now I have an '05 motor in my '98 and a ton of mechanic training. I drained the offending fuel and should be on the road tomorrow.

I would never have admitted this in a million years.

No but I always ask crashers/ stolen bike stories to tell what really happened. I am no hypocrate. This is what happens when a motor swap becomes easier than digging around.

If you say so. :)

Glad you found the problem.