PH BB Mechanics, help me!
Discussion
Help me diagnose my poorly 7R.
Poor running below 4krpm, wind the throttle on and it gets worse, to the point of cutting out. It then won't start for a few minutes (wet plugs at a guess). Once it fires up, you have to hold the throttle at a certain position till it revs cleanly through.
Once this has happened, you have to clutch it up past 4krpm and it runs fine.
I pulled my carbs apart hoping it was something simple, but nothing obvious apart from Dynojet needles and ever so slightly ovaled needle jets. I put the needles on their leanest settings but no joy, so I took the carbs off and put a second hand standard set on. It's still doing the same thing.
Assuming I've ruled out fuelling by fitting a different set of carbs, next up is the ignition system. I've got a pulse pick up coil, loom and CDI waiting to be trialled.
Am I missing anything glaringly obvious? Perhaps check the reg/rec- see if it's giving the CDI enough juice at low revs, split inlet rubbers (they did look alright, but it was only by glancing at them - gets a bit tedious taking the carbs off every 5 minutes)
Please help!
Poor running below 4krpm, wind the throttle on and it gets worse, to the point of cutting out. It then won't start for a few minutes (wet plugs at a guess). Once it fires up, you have to hold the throttle at a certain position till it revs cleanly through.
Once this has happened, you have to clutch it up past 4krpm and it runs fine.
I pulled my carbs apart hoping it was something simple, but nothing obvious apart from Dynojet needles and ever so slightly ovaled needle jets. I put the needles on their leanest settings but no joy, so I took the carbs off and put a second hand standard set on. It's still doing the same thing.
Assuming I've ruled out fuelling by fitting a different set of carbs, next up is the ignition system. I've got a pulse pick up coil, loom and CDI waiting to be trialled.
Am I missing anything glaringly obvious? Perhaps check the reg/rec- see if it's giving the CDI enough juice at low revs, split inlet rubbers (they did look alright, but it was only by glancing at them - gets a bit tedious taking the carbs off every 5 minutes)
Please help!
VidalBaboon said:
Nobody likes a split rubber. They looked good to me when I pulled them off, but will check again.
Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??
Surging can make a motor run all sorts of rough, do the revs hang before decreasing when you let off the throttle?Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??
Have you rejetted after fitting your new exhaust system?
Have you done anything to the breathers?
Yazza54 said:
VidalBaboon said:
Nobody likes a split rubber. They looked good to me when I pulled them off, but will check again.
Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??
Surging can make a motor run all sorts of rough, do the revs hang before decreasing when you let off the throttle?Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??
Have you rejetted after fitting your new exhaust system?
Have you done anything to the breathers?
The bike runs huge mains to compensate for the air recirc system on the exhaust. The bike was originally running mains suitable for a snazzy system but it made no difference having Keihin 180 mains or Dynojet 132 mains. Having the jets slightly out would never make it run this bad anyway, flatspot yes, but not this bad.
Edited by VidalBaboon on Monday 14th May 22:08
All 4 plugs are fouling, assuming I've ruled out any fuelling issue wih swapping the modded carbs for a standard set (the guy that's put the carbs in used to be involved with racing 7Rs in the 90s, so guessing he has a better idea of well set up carbs than me)
the only other thing that affects all 4 cylinders is the ignition, or as you say, a pesky air leak.
the only other thing that affects all 4 cylinders is the ignition, or as you say, a pesky air leak.
Have you tried new ht leads and fresh sparkplugs ? Had an issue like this but car related in an old vw. Low revs had a horrible vibration with no real pickup that seemed to get worse as you put your foot. High revs were much better but that could simply have been masking the issue. Checked all sorts and, after speaking to my local mechanic he recommended the above.
What was really odd was that there was no gradual deterioration. One minute it was fine and the next it was s
t.
What was really odd was that there was no gradual deterioration. One minute it was fine and the next it was s
t.Fouling plugs screams bad mixture to me. But the bad mixture could either be the carbs themselves or an air leak.
If all plugs are fouling but firing, it has to be something effective all four like you say, the leaves you with searching for air leaks or trying a spare CDI. I'd bet on it being a carb jetting/air leak issue though.
If all plugs are fouling but firing, it has to be something effective all four like you say, the leaves you with searching for air leaks or trying a spare CDI. I'd bet on it being a carb jetting/air leak issue though.
Edited by Yazza54 on Monday 14th May 22:17
VidalBaboon said:
Yazza54 said:
VidalBaboon said:
Nobody likes a split rubber. They looked good to me when I pulled them off, but will check again.
Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??
Surging can make a motor run all sorts of rough, do the revs hang before decreasing when you let off the throttle?Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??
Have you rejetted after fitting your new exhaust system?
Have you done anything to the breathers?
The bike runs huge mains to compensate for the air recirc system on the exhaust. The bike was originally running mains suitable for a snazzy system but it made no difference having Keihin 180 mains or Dynojet 132 mains. Having the jets slightly out would never make it run this bad anyway, flatspot yes, but not this bad.
Edited by VidalBaboon on Monday 14th May 22:08
Dynojet sizes are different to Keihin, and it has the emissions ste back on to lean the mixture out (somehow, black magic I assume).
You can (apparently) run an aftermarket system on standard jetting without any 'major' problems, I certainly had no issue swapping between standard and open can on the last one. If it was a jetting issue, it would have been cured by fitting the new exhaust.
te back on to lean the mixture out (somehow, black magic I assume).You can (apparently) run an aftermarket system on standard jetting without any 'major' problems, I certainly had no issue swapping between standard and open can on the last one. If it was a jetting issue, it would have been cured by fitting the new exhaust.
Edited by VidalBaboon on Monday 14th May 22:23
VidalBaboon said:
Yazza54 said:
VidalBaboon said:
Yazza54 said:
VidalBaboon said:
Nobody likes a split rubber. They looked good to me when I pulled them off, but will check again.
Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??
Surging can make a motor run all sorts of rough, do the revs hang before decreasing when you let off the throttle?Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??
Have you rejetted after fitting your new exhaust system?
Have you done anything to the breathers?
The bike runs huge mains to compensate for the air recirc system on the exhaust. The bike was originally running mains suitable for a snazzy system but it made no difference having Keihin 180 mains or Dynojet 132 mains. Having the jets slightly out would never make it run this bad anyway, flatspot yes, but not this bad.
Edited by VidalBaboon on Monday 14th May 22:08
VidalBaboon said:
No I don't think so, I did a float bowl mod (equalised the pressure between float bowl vent and airbox) but it ran exactly the same. So I've decided to go from square one and put it all back to standard.
Reet, read this (if you havent already) http://homepage.ntlworld.com/webzxr/zxr750r/Featur...With your mod it sounds like your jetting may now be too rich which would explain the plugs fouling and an unwillingness to rev until it clears its throat.
Has it always done this since you bought it or is it a new problem?
I thought it went pretty well when I had a go, apart from this issue causing it to cut out on me, so my money is on the electrical/CDI side (I'm no mechanic though
)
I still think it will be a good bike once this is sorted, it's just a case of finding the problem. Is it worth putting back to standard if none of the mods you have done have effected it?
I thought it went pretty well when I had a go, apart from this issue causing it to cut out on me, so my money is on the electrical/CDI side (I'm no mechanic though
)I still think it will be a good bike once this is sorted, it's just a case of finding the problem. Is it worth putting back to standard if none of the mods you have done have effected it?
Edited by CQ8 on Monday 14th May 22:39
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