Help General top end questions and vm34 settings...

[Brew]

So I've had my bike running for a few years but it has always had trouble doing more than 60mph. I just tore into the top end because I was ruining plugs on the left side really bad so I thought my rings were shot. that side was oily and the rings might be bad but the cylinder walls seem fine. There was quite a bit of oil in the head. I've never done a top end before so I don't really know what i'm looking at. Also I'm thinking my carbs have been set up the wrong way the entire time and thats was causing my 60mph top speed.? I'm going to have my carbs sonic cleaned and all new internals and want to know what settings you have for your vm34's. Also some ideas on my top speed issue. '79 with 2into1 mac exhaust no baffles and a pamco are the only mods. Also When I was doing my top speed it sounded like it started missing and not sure what that is a symptom of. maybe my advance is messed up? A little help would be nice. Trying to get it dialed in for bike week in a couple months.


Main Jet:
Pilot Jet:
Needle:
Needle Position:
Mix screw: In turns out.

 

[Brew]

here are a few pics...

 

[TwoManyXS1Bs]

Try the forum's advanced search, using "vm34" as the search and "grizld1" as the member.

 

[TwoManyXS1Bs]

On your left piston, pic #1, there's some scratches. Also, hard to see, but is part of the upper thin oil control ring missing/broken?

Check for scratches in the cylinder.

May be looking at pistons and bore job.

 

[Brew]

to the touch the cylinders are smooth and I think what you are seeing is the ring gap...

 

[TwoManyXS1Bs]

Had to zoom in. Maybe it's the lighting. Part of the upper oil control ring looked missing...

 

[NONclow]

So I've had my bike running for a few years but it has always had trouble doing more than 60mph. I just tore into the top end because I was ruining plugs on the left side really bad so I thought my rings were shot. that side was oily and the rings might be bad but the cylinder walls seem fine. There was quite a bit of oil in the head. I've never done a top end before so I don't really know what i'm looking at. Also I'm thinking my carbs have been set up the wrong way the entire time and thats was causing my 60mph top speed.? I'm going to have my carbs sonic cleaned and all new internals and want to know what settings you have for your vm34's. Also some ideas on my top speed issue. '79 with 2into1 mac exhaust no baffles and a pamco (without the E-advance I guess?) are the only mods. Also When I was doing my top speed it sounded like it started missing and not sure what that is a symptom of. maybe my advance(?) is messed up.

Carb issue. Maybe sync, float, or jetting . Same jets in both carbs?

Sounds like the left carb is flooding and washing the oil off the cylinder. The piston dome, and skirt are visibly not as dark as the right (the heavier scratching, also, like Two Many noticed!). Compression test performed before teardown (fingers crossed)? Measure the bores (or have them measured with adequate tooling ) to decide if they can be honed/deglazed and stock dimension pistons and rings can be used (pistons only could be cleaned and reused [this guy'd be for replacement though] if within tolerances), or if an oversize is nessesary. Then purchase pistons before machining, then the cylinders can be matched to the pistons.

If advance is stock fly weight setup I would service at this time also.

I personally haven't experienced the VM34's..........yet. So:

Try the forum's advanced search, using "vm34" as the search and "grizld1"

 

[grizld1]

Give the motor a full inspection (there's no point in putting the head back on if it needs a valve job, new rods, etc.); if the motor has been run much on thinned out oil you could find more grief. But don't assume that; the wet piston could be due to other things. For clearance specs on pistons and valve guides, side play on rods, ring gap, etc., go to www.biker.net for a free download of the factory manual. For help on carb tuning, look around; it's all been done before.

 

[Brew]

Thanks everyone. I downloaded the factory spec stuff and will give it a full inspection. Any ideas on my 60-65mph top speed issue?

 

[650performance]

Griz is right. You have to really get into it and see what's going on. The top speed problem is entirely related to whatever is wrong with the engine. Get the engine more or less right and it will no longer be a problem. (I'm assuming, of course, that a brake(s) isn't dragging, etc.)

 

[grizld1]

Brew, with all due respect, nobody can troubleshoot your motor based on the information you've supplied--no info on current jetting, no compression numbers, only the fact that the engine misses at speed, with no indication of whether the misfire is related to rpm or throttle setting. Guys will probably heap the BS high on why you're down on power, but I'd be surprised if you got anything useful out of it. The best advice I can give you is to take your motor to a shop where somebody knows what he's doing and have it gone through.

 

[Brew]

I get it. I should have checked a few things before taking it apart but I was expecting it to be really bad rings and was very surprised and kinda pissed to learn that my problem might be elsewhere. Oh well I got two months to figure it out before Daytona. Thanks for all the input

 

[chizler62]

If you brought your cylinder, pistons and head into my shop. I'd 1st say your "oily problem and top speed issue is mechanical" of course I'd measure them to be sure.Tho, It's clear from the piston wash that it's most unlikely that its jetting or a carb issue. Plus you can see the piston's Y axis has worn the blow by stain off the skirts.
Appears your air filters are gauze type and are dry? You should keep them oiled.
My suggestion, don't mess with carbs at all. Send the cylinder out to be bored next size and get new valve guide seals put in and head chamber cleaned up. Reassy and see. I bet your problems are gone.