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78 550 bogs 8 - 9k rpm and after redline shift

  • Thread starter Thread starter joshjosh
  • Start date Start date
J

joshjosh

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So, I just had my carbs "professionally" cleaned at my local classic japanese m/c shop and I'm not sure all is well. Here's some history.

Carbs : Had them completely rebuilt about 8 years ago, first time I've touched them since.

Fresh points, condensors, valve adjustment, and a fresh battery before the start of last season

Haven't cleaned the air filter this year, but did last year, and did a visual and it looks fine.

Stock plugs, look a little lean if anything to me, but I'm used to running rich.

Timing is a TINY bit off, gonna reset it this evening with the gun.

So I decided that it was long overdue for a carb rebuild, even though the bike ran reasonably well, just a little weird cold, a little rich, and had leaky o rings that put gas in the crankcase occasionally. Time for a rebui;d.

Anyway, now the bike has trouble pulling past about 7500-8000 to redline at 9000. Sounds like a flag flapping in the wind somehow, sort of sputtery. Previously it pulled well, right into the red :oops: .

Also, after shifting off WOT, when hitting the next gear at WOT it bogs briefly before catching.

Otherwise, idles nicely, takes a little longer to warm up to get off the choke, I'm guessing that's because it's no longer running rich. And midrange power is fine.

So, as the only thing that's changed is the carbs, I'm guessing that's where my problems are. Any ideas what I should go at the mechanic with for troubleshooting?

Thanks guys
 
The only other thing is I just realised the gas is from January, and is unstabilized. Maybe I'll get some fresh stuff in there and see if it makes a difference, but I appreciate any input.
 
joshjosh said:
So, I just had my carbs "professionally" cleaned at my local classic japanese m/c shop and I'm not sure all is well. Here's some history.

Carbs : Had them completely rebuilt about 8 years ago, first time I've touched them since.

Fresh points, condensors, valve adjustment, and a fresh battery before the start of last season

Haven't cleaned the air filter this year, but did last year, and did a visual and it looks fine.

Stock plugs, look a little lean if anything to me, but I'm used to running rich.

Timing is a TINY bit off, gonna reset it this evening with the gun.

So I decided that it was long overdue for a carb rebuild, even though the bike ran reasonably well, just a little weird cold, a little rich, and had leaky o rings that put gas in the crankcase occasionally. Time for a rebui;d.

Anyway, now the bike has trouble pulling past about 7500-8000 to redline at 9000. Sounds like a flag flapping in the wind somehow, sort of sputtery. Previously it pulled well, right into the red :oops: .

Also, after shifting off WOT, when hitting the next gear at WOT it bogs briefly before catching.

Otherwise, idles nicely, takes a little longer to warm up to get off the choke, I'm guessing that's because it's no longer running rich. And midrange power is fine.

So, as the only thing that's changed is the carbs, I'm guessing that's where my problems are. Any ideas what I should go at the mechanic with for troubleshooting?

Thanks guys
Click to expand...

Leaky O rings putting gas in the crankcase makes no sense. It's a bad petcock if that happens.

What did you change that would make it too lean at WOT?

Same jets or were they changed? Float level adjusted? There's not much else that effects WOT, unless somehow not enough fuel is getting to the carburetors. Kink in the vacuum line or in the fuel line? Small split in the vacuum line?
This could possibly be a fuel tank vent issue?.. but I doubt it.

Are you running stock intake and exhaust or something else? If something else were the carbs jetted correctly for that?
 
I honestly don't know what the main jet was previously, but I have a sneaking suspicion what's in there now isn't the same. The bike has the same 4 to 1 and tiny vance and hines can it's had on it for the last 6 years, back when it ran great.

As far as the fuel in crank, what would happen is after sitting for a few days, sometimes the carbs would be dry, and I'd have to crank it for a while to get some fuel in there, other times it would start in a split second. The more often I went out and the carbs needed to be primed, the more the oil was a little gassy.
 
I'd start with putting the original jets back in if it worked fine with them. It was probably jetted correctly with them and now it's not. My 550 has 80 main jets stock, I have 110 in it now with a Kerker pipe and K&N pods, but I live at 6,000' too. You willl probably need bigger jets.

What size main jet was in it before?
 
Yeah that 80 main jet in that kit is way too small for a 4-1 pipe.

Do you still have the old ones?


And how long were you leaving it on Prime?
 
I hope the shop kept the old jets. Thanks a lot for the info, I had a feeling it might be something along those lines. I'll be having a chat with them on the weekend I think.
 
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