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Post by maicohunter on May 1, 2008 1:25:21 GMT -5
Mystery to me. The bike starts up only with choke.Once its running i can take her out and she pulls through all the gears smooth. Once warmed up i let it idle and it will hold at 1100 for 30 seconds at most before it either stalls or if i give it some throttle theres a intermitent miss or pop.I have checked the valve clearance's,perfect.Checked the timing,dead on.Dis assembled the carb and its clean as can be.This leaves me with the CDI,coil,  ? anyone had this problem. The bikes runs great except for this anoying miss.Its not backfiring its just a light popping inside the motor.... Thanks |
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Post by aero on May 1, 2008 5:10:41 GMT -5
It sounds like a carb problem. The typical SR one that gives the bike its poor rep for hot starting.
I have found two ways to cure it. First, get a full carb repair kit that has all the rubber diaphragms, new idle air screws and jets and clean out all the jetways with a carb cleaner.
Or more extreme: Replace the Carb with a Mikuni VM34 (or 36 if you want a little more power). You'll have to price up the two options where you are in the world. It can work out that a new carb isn't a great deal more expensive then all the parts for a rebuild.
The Mikuni VM34 gives excellent starting hot or cold and is a much simpler animal with out all the fussy valves and diaphragms.
If the bike starts and runs, pulling through the gears, the ignition is working as advertised.
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Post by stevec5000 on May 1, 2008 9:22:07 GMT -5
Or instead of replacing the carb use a Colortune and set the idle mixture properly.
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Post by olddog58vette on May 2, 2008 14:27:21 GMT -5
It sounds like a carb problem. The typical SR one that gives the bike its poor rep for hot starting. I have found two ways to cure it. First, get a full carb repair kit that has all the rubber diaphragms, new idle air screws and jets ..... Where did you find or buy a full carb repair kit? Thanks ;D |
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Post by chew652 on May 2, 2008 15:08:17 GMT -5
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Post by aero on May 3, 2008 3:34:28 GMT -5
Or instead of replacing the carb use a Colortune and set the idle mixture properly. That's an option, but you'll be able to get the mixture spot on even with perished/holed/hardened diaphragms and worn jets. I've had carbs on off, stripped and reassembled so many times I've got to the point where I was ready to launch them into nextdoor's fish pond. A single is pretty easy to find the mixture 'sweet spot' without a colour tune though. The range between hunting and labouring is very marked. Much easier to spot then on a multi cylinder engine where the other cylinders tend to drive on the one thats running off. But check first before spending cash that someone hasn't being fiddling with things they know 'owt about I got mine from A yamaha dealer in Germany, the eBay shop items looks like the same kit, the price is about the same. |
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Post by stevec5000 on May 3, 2008 9:20:48 GMT -5
>That's an option, but you'll be able to get the mixture spot on even >with perished/holed/hardened diaphragms and worn jets.
Yes, but that's only if it's close to start with. In the case of the original post he doesn't know if it's too rich or too lean so he needs some place to start and the Colortune would give him an indication of what's going on so he will know how to adjust.
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Post by aero on May 3, 2008 14:23:32 GMT -5
I always say check the simple stuff that doesn't cost first....
but having never owned a colour tune in 25 years of riding twins and singles, if you can't get it to accelerate off idle the simple thing to do is apply the choke.
If it runs a whole lot worse you know its running way too rich. If it runs better, then gets worse the more choke you apply it was too lean.
If things get more out of hand then that I take it to a guy who has a rolling road. (although I've only had to do this when recarbing, with standard stuff its easy enough to sort out)
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Post by maicohunter on May 9, 2008 23:43:29 GMT -5
Thanks guys,I have disassembled the carb,its in great shape,diaphrams and all.Current jetting is 300 main,25 pilot. Thats what my book states as the stock setup.The plug looks tan,not to rich and not to lean. I did notice some weeping around the head gasket ! oily film. Could the head gasket be blown ? that might explain the occasional pop.It really pops alot on deceleration.Again it only starts with the choke never without.I used my compression gauge on it and it feels like it has a ton of compression yet won't register over 35 psi. maybe my gauge is malfunctioning......anyone....Thanks
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Post by stevec5000 on May 10, 2008 8:52:21 GMT -5
If it pops a lot on deceleration that means it's too lean and you need a larger pilot jet. Or maybe yours is partly clogged or you have holes in the muffler. Weeping a little oil around the head gasket seems normal since mine does it too. It's hard to get an accurate compression reading on a motorcycle engine with a car gauge since the volume is so small and the gauges tend to leak. I had to try several different ones before I found one that would work accurately.
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Post by caferacercarl on May 11, 2008 2:43:39 GMT -5
Our pilot jet in aussie was much bigger than a 25, steve's right, lean, try a 35! and about 2 and 3/4 turns out on the mixture screw and see how that goes. [or 2 aspirin and ring me in the morning]
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Post by maicohunter on May 11, 2008 8:36:53 GMT -5
Ok,Heres the latest.And bye the way i thank all of you that have posted.I once again took the carb apart,blew out everything.Swapped out the 25 pilot for a 30.Reinstalled everything. Started her up and she ran flawlessy for 20 min. Great smooth idle.No popping,no miss. 20 min. into it it started all over again.I think some old foam airfilter fragments are getting sucked into the pilot venturi and may be blocking the air intake on the idle circuit. Im taking the carb off again this morning and i hope that what i find because its driving me crazy !
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Post by Sleipner on Jul 12, 2008 19:56:42 GMT -5
Sounds exactly like the same problem that I've had with my bike. It idles fine at first but once it get hot it misfires and dies at deceleration unless I gently give it some throttle.
Were you able to solve the problems on your bike?
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Post by solo2racr on Jul 12, 2008 21:09:28 GMT -5
It's hard to get an accurate compression reading on a motorcycle engine with a car gauge since the volume is so small and the gauges tend to leak. I had to try several different ones before I found one that would work accurately. I would have to say that it was just leaky gauges. 500cc Single = 2litre 4cyl. Pretty common displacement for autos. |
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kena
New Member
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Post by kena on May 23, 2024 12:51:53 GMT -5
Ok,Heres the latest.And bye the way i thank all of you that have posted.I once again took the carb apart,blew out everything.Swapped out the 25 pilot for a 30.Reinstalled everything. Started her up and she ran flawlessy for 20 min. Great smooth idle.No popping,no miss. 20 min. into it it started all over again.I think some old foam airfilter fragments are getting sucked into the pilot venturi and may be blocking the air intake on the idle circuit. Im taking the carb off again this morning and i hope that what i find because its driving me crazy ! Im having a similar problem. Did you ever find the solution? |
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? anyone had this problem. The bikes runs great except for this anoying miss.Its not backfiring its just a light popping inside the motor.... Thanks
