Carb trouble/exhaust Popping.

[normski]

Hi, I have been a member for some time, but never made a post or introduced myself - So Hi ALL a belated merry exmas and all the best for the new year.
The reason for my post is - I've a 1977 B GT750, Although its in very good condition, its popping on Number 1 (L/H) cylinder. I have checked the Points and Timing, renewed the Plugs, checked the compression and Fuel/air mixture 3/4 turn out, balanced the carbs as per Suzuki instructions etc. But still it Pops!. I have now stripped down the carbs and found that the Needle has Y48 stamped on it - whatever that is!! according to Robert's Foundry - should be 4DN18. And that all three carbes has a #110 Main jet which I am lead to believe that Number 2 cylinder should be #107.5. Could anyone confirm the jet sizes and shed any light on the NEEDLES Y48?. and may be the Popping - Thanks.

[bigrocketrider]

Have you just bought it? If not, and it ran fine before, I doubt it would be caused by the jet/needle difference. Popping would more than likely be a blocked pilot jet I should have thought.

[canaletto5]

Hi, I have been a member for some time, but never made a post or introduced myself - So Hi ALL a belated merry exmas and all the best for the new year.
The reason for my post is - I've a 1977 B GT750, Although its in very good condition, its popping on Number 1 (L/H) cylinder. I have checked the Points and Timing, renewed the Plugs, checked the compression and Fuel/air mixture 3/4 turn out, balanced the carbs as per Suzuki instructions etc. But still it Pops!. I have now stripped down the carbs and found that the Needle has Y48 stamped on it - whatever that is!! according to Robert's Foundry - should be 4DN18. And that all three carbes has a #110 Main jet which I am lead to believe that Number 2 cylinder should be #107.5. Could anyone confirm the jet sizes and shed any light on the NEEDLES Y48?. and may be the Popping - Thanks.

I would check/change the condensor. Popping is usually misfiring due to erratic spark, not fuel.Kev

[willowden]

Funnily enough I had the same issue with my 750B.
Baz refurbed my carbs & it still did it.
I fitted Accent electronic ignition & it still did it.
Turned out to be the head gasket blowing over into number one.
I was then that happy with the result........ I sold it !

[Kettletimes3]

Popping can also be an air leak in the exhaust.

[apwrigs]

I would agree with Canaletto, most probably a dodgy condenser for sure. Happened to me recently, popping is usually electrical. Changed the condenser and problem solved.

[normski]

Hi Willoden. No the needle turns out to be North American (different emotions) so I have bought some UK ones and refurbished and had the cards sonic cleaned.

I'v also put a new cylinder head gasket on but the original one looked OK when I took it of , so i doubt it was that.

I have tested the Condenser and it checked out OK - same as the others (can't remember the value off hand) and besides the points usually spark with a dodgy Cap, had the trouble on a Kawi.

I must say that the leaky exhaust my have something to do with it as I've found a failed thread on on of the exhaust screws and had to take the cylinders of and get it repaired.
Just putting the engine back together and waiting for some parts from Robinsons. So will be a a week or two before i can try again.

Dose any one Know about the MAIN JET in the number 2 Carb - should it be #107.5 as I have read ????

Thanks ALL for your input will Keep you posted.

PS. Happy New Year to you ALL.

[apwrigs]

Hi Normsky, without stating the obvious, are the condensers wired correctly, I.e the metal tabs in the right position against the insulating washers, if not that would give you a weak spark and popping.

[normski]

Hi Aprig. Sorry for the delay, yes they are in the correct pos, and not touching the other part of the point bracket - which is easily done and shorting it down to the casing /Negative.

- Still had no reply about the Main jet #110 or #107.5?????

[teazer]

Center main jet with stock exhausts is one size down from the outer pair, so 110 in 1 and 3 and 107.7 in #2 should be just fine.

With chambers, all three should be the same.