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Posted (edited)

Well, after getting my '87VR back together I had 2 stuck carb needle/seat assemblies. So I decided since the old girl had over 70k...it was time for a complete going thru of all carbs. I have put 99% of all the miles on this bike. So I know how it should run. I have done carb work many times on many different bikes. So I was not afraid. Jets were removed, jet blocks "dipped". I set the floats absolutely perfect on the bench and confirmed w/engine running. Results have been all carbs give an ideal idle of 2.5ccw low speed screw all carbs. While #1 & 2 cause rpm drop right at 3 ccw. Which is quite normal to me. BUT on #4(rght. frnt) I can go to 5 turns ccw and not cause the idle to drop and #3 is almost the same. Which is not normal to me. All settings done with an accurate digital tach. Carbs are syc'd.All checks for vacuum leaks done. None found nor suspected because... HERE's the real issue. #4 starts to misfire when the bike is really hot, seemingly like too rich. I can hear the spark cap arcing and using a screw driver and my finger(ouch)confirmed this. Wire replaced 2 times, spark plug & cap(stock and NGK) 3 times-no change. The spark plug is not wet when it is removed. But does have a very small brown spot on it. I suspect something like this may be impossble to read w/o that glass spark plug thing(can't remember the name).I honestly believe the new internal gaskets that are now the "norm", don't seal worth a damn. These new cheapo gaskets are very fiberous.I suspect they don't seal well. The originals were hard paper. Does anyone else whose done rebuilds have the same suspicions regarding these NEW gaskets...? My only other possibility is the choke plunger leaking. But this possibility is something I have never witnessed in all my years. Lastly , I used to always get over 40mpg solo... Now it's impossible. No, I am not going to lower the needles. That's not the issue here.

Edited by jasonm.
Posted

Just my inexperienced guess, but I would suspect #4 valve gap too tight, and as valves expand with heat, #4 does not close completely for entire required cycle(compression or power).:2cents:

Posted (edited)

Thanks, But I don't think Valves would cause this. Because tight valves cause lack of compression and thus less intake vacuum...aka less fuel. Also the valves all were check by me @ 66k. Now have 74k. THIS IS a probable gas foul misfire issue...ARCING...zap zap can't burn the gas. I think I need a colortune thingy to know absolutely. But rule is...if you cannot burn it and zapping happens...it's too rich. I am trying to find anyone with possibly similar issues after a carb rebuild.

Edited by jasonm.
Posted

If the problem truly is the gasket... one could make them from gasket material from your local auto parts store. Pull one of the old ones and make four copies. I'd do it for my bike, but I'm just too darn lazy to do it right now. I'd rather buy the gaskets, but haven't seen them anywhere.

Posted

The gasket material at the auto parts store is no better than the Yamaha ones. The gasket is same as the old Vmax. And still available. I have spares still of these Yamahas. But why continue use something I believe is inferior to the original from 1987. ALSO I have changed the spark plugs 3 times. And now to help lessen the misfires, I and am now using NGK non-resistor type plugs on all and a 5k ohm NGK cap on #4 instead of the 10k stock. Any other ideas?

Posted

Another solution to making gaskets... if you have a spare... lay it on a white piece of paper and draw the inside and outside pattern (and any holes in the gasket).

 

Then take it to a laser xerox machine and run off as many examples as you need. Now the laser uses a plastic that is fused to the paper so it works backwards... lay the paper (black outline to the new gasket material) and run your wife's iron over the top. The platic will transfer to the gasket material and you can just cut it out...

 

Of course this also works for transferring patterns to material to be custom sewn (jackets, shirts, etc.). The plastic washes out later.

Posted

most interesting. But I am still not going to tear the carbs off just yet....till I hear a bit more possibilities from others as to my possible causes for this odd #4 issue. I jumped head 1st into rebuilding the carbs which likely did not need everyhting I did. Now I am taking a cautious factual approach. I guess I may buy a "colortune" . But for this one issue I am not sure? Let me know what you all think...

Posted

Well, I went on Ebay. And on Tuesday ordered/won a Colortune for 12mm spark plug engines. NOW the bad news. The damn volcano in Iceland has likely stopped the Colortune from shipping. Talk about bad timing. The seller has not updated me on anything regarding, if this got shipped shortly after I "won" this. Their normal site info says something like this, "expect 7 days for shipping, coming from UK." Someone up there hates me.:95:

Posted

While you are waiting, it would be a dandy time to do a compression check and write those numbers down... that would detail any valve or ring problems.

Posted

that's a good idea. I did Dyno my bike 4 years ago 93hp @7000rpm. In fact have had it done 4 times on 2 different dynos...always 93+hp. And 80+ft/lbs torque at most any rpm up to 5500 . Still waiting for reply from the seller. Just wish someone had a colortune near me...

Posted
Well, I went on Ebay. And on Tuesday ordered/won a Colortune for 12mm spark plug engines. NOW the bad news. The damn volcano in Iceland has likely stopped the Colortune from shipping. Talk about bad timing. The seller has not updated me on anything regarding, if this got shipped shortly after I "won" this. Their normal site info says something like this, "expect 7 days for shipping, coming from UK." Someone up there hates me.:95:

 

I dont have faith in the colortune couldnt really tell a color change that well.

Posted

It's a $40 colortune or an expensive EGA machine. The idea for me is to not have to guess after I probably go thru the carbs for the 3rd time ...whether or not #4 is too rich. If it's orange=too rich. This takes a lot of time off trouble shooting. Others have used them. I have not heard any complaints. If anyone having a colortune has any user helpful hints ...email me.

I really went thru all of them w/ "fine tooth comb" as they say. They were clean to start with. But had them apart to change needles/seat assemblies and said..." this is nothing new to me, what the heck". I am not a novice at this sort of thing. So I know I have an issue. I posted a "knocking noise" from my water pump a while back. NOW I suspect even though my carbs are sync'd perfect. Having #4 very rich is not allowing it to idle as smooth as possible. Jusy hoping the colortune shows up by end of the week.:fingers-crossed-emo:fingers-crossed-emo

  • 4 weeks later...
Posted

Latest update: I got the colortune and did not show me anything. Everything is "blue". I also made sure the choke plunger were good and seated properly. I won't go into details on this choke check. But something just ain't right. I know it's rich on #3 & 4 . As it misfires when idling for long periods and just by reving it the misfire stops and runs clean for a while(few minutes). And as a test> the spark caps when a grounded screwdriver is placed near them...I get a 1/2" arc. Meaning it rather jump to a grounded screwdriver than the small gap on the spark plug within the engine. #1 & #2 do not do this. No, I do not normally idle for long periods. But this was 1st noticed when I was syncing the carbs last year after the carb rebuild. Then removed the carb sync and it did not go away. As stated before. ALL ignition items replaced that are easy to reach. Right now, I will possibly remove the carbs and replace the pilot gas jets. I did remove and clean the gas pilots during rebuild process. Maybe they are not seated correctly. Which sounds impossible. Since I tightened them good. Could I have cleaned them too much? They are expensive from Yamaha. But there are other suppliers like Sudco.

Posted

I suspect you MEAN the idle-low speed screw oring leaking. Ok, ALL orings and gaskets have been changed including that one. FYI- that brand of rebuild kits I have been using for years. The jets are cheap and NOT machined like OEM mikuni jets, but the gaskets and orings are good.

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