Well, here we go again.

[Demonsinmysemen]

Hey, all! Jon here for another episode of: what the hell! Here's the what's happening; bike runs strong whenever I start her up. Starts fine. No problems. No need for choke. Vboost works. Battery charges okay. The problem is whenever the temp gauge gets up to about 75%. The idle starts to get a bit jumpy and if I don't give her some gas, she'll eventually shut off and I'll have to wait about minute or two before I can turn her back on. So long as I'm not stopped, she'll run strong. One thing I noticed is that it never gets hot enough to turn on the fan. I was suggested to swap out the voltage regulator so I did with no changes other than it seems to start up a tiny bit easier. Any ideas?

 

[one2dmax]

No need for choke? It's too rich and warmed up may cause the stumble as it's drowing. BUT, I would check the running/charging voltage when it's not running well.

 

[user 16790]

mine was like you describe when hot, I fitted new ht leads, plugs and caps, all good now

 

[Demonsinmysemen]

No need for choke? It's too rich and warmed up may cause the stumble as it's drowing. BUT, I would check the running/charging voltage when it's not running well.

The bike should be choked all the time?

 

[Demonsinmysemen]

mine was like you describe when hot, I fitted new ht leads, plugs and caps, all good now

HT leads? Spark plugs. Caps?

 

[one2dmax]

It should need choke to start unless the engine is already somewhat warmed up. If from a cool or cold start you don't need a choke to start or run somewhat decent you are set too rich.

 

[user 16790]

HT leads? Spark plugs. Caps?

spark plugs, spark plug caps, spark plug to coil ht leads (cables), mine was arcing out when it got hot

 

[Demonsinmysemen]

It should need choke to start unless the engine is already somewhat warmed up. If from a cool or cold start you don't need a choke to start or run somewhat decent you are set too rich.

Well, it is really hot in Miami. I don't know if that would change anything. Hot enough that I can't really touch the bike from the heat burning me. I haven't tried night riding in a long time in fear of getting stranded. I think you're most probably right though.

 

[Tasker]

Most likely pilot air too ritch or float levels incorrect.

 

[Demonsinmysemen]

spark plugs, spark plug caps, spark plug to coil ht leads (cables), mine was arcing out when it got hot

Where can I get a set? I've looked everywhere except like partzilla. I usually only find some universal type. Could you shoot me a link if possible?

 

[Demonsinmysemen]

Most likely pilot air too ritch or float levels incorrect.

Damnit, I just cleaned them. Well, gotta do my valves so I'll take advantage of having them off. Think I can lean it out without jetting? You know the measurements of the floats? I think someone told me something like 1/16 of an inch.

 

[user 16790]

Where can I get a set? I've looked everywhere except like partzilla. I usually only find some universal type. Could you shoot me a link if possible?

I got mine from a UK company called EXACTREP http://exactrep.com/acatalog/index.html
you might be better off talking to Sean Morley as he seems to be a great provider of vmax parts in USA,
I'm not saying it will fix your problem but it fixed mine and your 'issues' sound similar to what I had, good luck

 

[Demonsinmysemen]

I got mine from a UK company called EXACTREP http://exactrep.com/acatalog/index.html
you might be better off talking to Sean Morley as he seems to be a great provider of vmax parts in USA,
I'm not saying it will fix your problem but it fixed mine and your 'issues' sound similar to what I had, good luck

Thanks a lot for all that info. Super helpful. Sean and I have been back and forth. The man loves to help. He believes that it is a symptom of too rich carbs, which makes perfect sense. Gonna check for the cables for arcing. I'm not knowledgeable on tuning carbs, so I'm hoping it's the same as your Vmax.

 

[uncebanyo]

Sounds like it might be running too rich, but check the plugs to verify this. If it turns out to be running lean, you might have air leaks that open up when the engine heats up. I had very similar symptoms on a different Yamaha ('82 XJ750). Started up and ran great until the thing heated up. Turned out the carb boots where they meet the engine were cracking open when hot, sucking in extra air. But when cold they shrunk back down and sealed tight. Took me forever to figure out.

Best way to check for this is to heat up the bike, then let it idle and spray a little bit of starting fluid around any areas where there could be a leak (avoid the actual air intake). If the engine sucks in the fluid through a leak, it will rev up, confirming that there is an air leak.

'Course, if you check your plugs and the engine is running rich, air leaks aren't your problem. Just thought I would chime in with my experience. It was a very frustrating issue to isolate.

Good luck.

 

[sdt354]

Where can I get a set? I've looked everywhere except like partzilla. I usually only find some universal type. Could you shoot me a link if possible?

Why not upgrade to COPs instead now? More reliability and simplistic.

 

[dannymax]

Clean your existing spark plug caps, trim 1/8" - 1/4" off either end of your plug wires (to clean copper), clean the carbs and you should be GTG.

Here's the plug cap for reference

 

[dannymax]

Why not upgrade to COPs instead now? More reliability and simplistic.

I like coil sticks too Steve-o, nice & simple. Trouble with most of what you buy now (unless you buy brand new ones) is they are the ones recently replaced cuz they're already old, tired and reaching the end of their useful life.

Do the maintenance on the OEM caps and wires first....there's a good chance you will be very pleasantly surprised with the results.

Or get hold of Sean, he has brand new coil sticks (COPs) for sale, with 'Hot Start' testing already done on a prototype.

 

[Demonsinmysemen]

What are cops?

 

[Demonsinmysemen]

Sounds like it might be running too rich, but check the plugs to verify this. If it turns out to be running lean, you might have air leaks that open up when the engine heats up. I had very similar symptoms on a different Yamaha ('82 XJ750). Started up and ran great until the thing heated up. Turned out the carb boots where they meet the engine were cracking open when hot, sucking in extra air. But when cold they shrunk back down and sealed tight. Took me forever to figure out.

Best way to check for this is to heat up the bike, then let it idle and spray a little bit of starting fluid around any areas where there could be a leak (avoid the actual air intake). If the engine sucks in the fluid through a leak, it will rev up, confirming that there is an air leak.

'Course, if you check your plugs and the engine is running rich, air leaks aren't your problem. Just thought I would chime in with my experience. It was a very frustrating issue to isolate.

Good luck.

So I was taking off the carbs and noticed that it was strangely easy to take off the carbs. I was going for a valve adjustment (my bike is at 18,000. It sounds like the valves kinda get stuck at a low rpm until I open up the throttle). I imagine it has a lot to do with what you just said. I have been studying and haven't gotten around to checking out the forum.... I feel kinda dumb.

 

[Demonsinmysemen]

Sounds like it might be running too rich, but check the plugs to verify this. If it turns out to be running lean, you might have air leaks that open up when the engine heats up. I had very similar symptoms on a different Yamaha ('82 XJ750). Started up and ran great until the thing heated up. Turned out the carb boots where they meet the engine were cracking open when hot, sucking in extra air. But when cold they shrunk back down and sealed tight. Took me forever to figure out.

Best way to check for this is to heat up the bike, then let it idle and spray a little bit of starting fluid around any areas where there could be a leak (avoid the actual air intake). If the engine sucks in the fluid through a leak, it will rev up, confirming that there is an air leak.

'Course, if you check your plugs and the engine is running rich, air leaks aren't your problem. Just thought I would chime in with my experience. It was a very frustrating issue to isolate.

Good luck.

The boots were definitely loose, funny enough. The problem persists but it seemed to run a bit better. Tried to sync the carbs afterwards,#4 will not sync correctly. The rest hang out at around 20 cmhg versus #4 which hangs around 40. Quite a bit off. What could that indicate?