Main jets on American import

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barney01
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Re: Main jets on American import

Post by barney01 »

+1 with Baz. The 550 is the same it's the conditions that are different. Climate/altitude affect the running. American bikes had different jetting because of emissions laws only. Balancing the carbs with airflow meter drastically improved the running for me.
Just remembered that US carbs had a different serial number but I don't know how they differed.
NO SMOKE .......NO POKE
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Keithfgb
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Re: Main jets on American import

Post by Keithfgb »

Hi Baz, what flow meter would you recommend for an amateur like me to buy? After dropping the needles the surging on overrun is better but it’s running lean. If I can’t get it correct soon the bike is getting sold!!!
It'll go eventually.
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BAZ
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Re: Main jets on American import

Post by BAZ »

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Keithfgb
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Re: Main jets on American import

Post by Keithfgb »

Thanks, I’ll get one ordered then you can tell me how to use it. I’m open to all advice here as I’ve tried everything else and after the amount of work that’s gone into the bike it’s a shame I can’t get it right.
It'll go eventually.
barney01
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Re: Main jets on American import

Post by barney01 »

NO SMOKE .......NO POKE
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Keithfgb
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Re: Main jets on American import

Post by Keithfgb »

All attempts at curing the surging/bucking on override have failed. Yes that’s correct,I’m a dismal failure,I admit it. I’ve tried everything I can think of. There has been some great advice given on this forum and others. All have failed. The b——— d thing will not do as it’s told. So after all the hard work that has gone into the bike it had now gone!!! Well,to Barry’s house anyway,Allan and I dropped the bike off today. Jeez them two can talk,ive got ears like lumps of liver listening to the two of them. It was a privilege to meet Barry after all this time. So,hopefully the bike will be rideable for next weekend. Fingers crossed.
It'll go eventually.
teazer
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Re: Main jets on American import

Post by teazer »

Surging on closed throttle is caused by either rich or too lean. Both cause surging but lean tends to be worse.

The fix on BS40 is to drill and tap for a smaller air jet. On those stock is 1.0mm and we fit 0.9 or 0.8 to correct that lean spot.

On slide carbs it suggests that the pilot air jet has been poked around or drilled out to clean it by a PO. If there's enough metal, I'd do the same mod to those carbs.

While you are in there, check flow with a can of WD40 to see that the bypass is clear on all 3 carbs and to be sure they all flow more or less the same.
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Harrymail
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Re: Main jets on American import

Post by Harrymail »

I've just finished running my 550 in after an engine rebuild. Now I'm able to go faster I've found I have surging too. Most noticeable when shutting the throttle off from higher speeds. Bit scary on a bend. Have to pull the clutch in. Sounds just the same as you Keith. Carbs are rebuilt ones from Baz. I've got an air flow meter so will be checking the balance first. At present they are as Baz set them statically. Will be interested to hear what happens with yours Keith.

Paul H.
Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
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Keithfgb
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Re: Main jets on American import

Post by Keithfgb »

That was exactly what was happening to mine Harry. It got to the point that I did not want to ride the bike as I could not feel safe going into corners etc. It was also difficult to keep a steady throttle at 3 to 4 thousand revs. I will let you know what Barry diagnoses with mine and hopefully it will help you.
It'll go eventually.
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Harrymail
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Re: Main jets on American import

Post by Harrymail »

Keith

I balanced my carbs yesterday with an air flow meter. My readings on the meter were 1.5, 1,5, 2.5 on a scale of 0 to 5. So the RH carb was a good bit out. Needed a full turn on the adjuster.

Good news is the surging has completely gone. Hope you have the same success when they come back from Baz.

Cheers

Paul H
Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
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