Only running on one side

jerry · 07-10-2024, 04:52 PM

750ss finally running again after 3 years of renovation ,, But only firing on Vertical cylinder ,,

Horizontal has spark at plug and coils and ignighters are fine I swopped them around to test ,, there is fuel in carb too but not going bang on that cylinder ??????

Now the carbs have been stripped , Ultrasounded, cleaned and rebuilt with all new seals etc float valve set same on both carbs ,, no leaks or overflowing ?

Did it all just like on all my other rebuilds and these carbs have been serviced by me 3 times in last 16 years , so Im not sure now what to do next other than open that carb up again and have a look ????

Mark64 · 07-10-2024, 07:01 PM

Electrics is favourite, swap plugs & other components to prove

jerry · Today, 10:38 AM

OK Swopped plugs , HT cables , coils etc but no change all electicals working correctly nice big sparks ,, but horizontal cylinder still not running just spit backs ,, so it must be carb related .. ho hum .. ???? carbs coming off to check ????

utopia · Today, 12:33 PM

I know you're very familiar with these engines and their foibles but I can't help wondering how long you have cranked it for and/or left it running on just the one cylinder.
My own M750 always take ages to fire up properly on both cylinders after a long lay-off and this seems to be related to the float bowls taking an absolute age to refill after their former contents have evapourated.
It is often the case that one cylinder will fire and run for 30 secs to even a full minute (at least it seems like that long) before the second cylinder will kick in.
I assume this is while it is trying to fill the float bowls, which seems to take an awfully long time even on the first cylinder to fire and an absolute age on the second cylinder.
Of course my fuel pump is original and therefore may not be operating at full efficiency after 25 years of diaphragm deterioration, which may be a contributory factor.
Anyway, long story short, it might be worth letting it run for a little longer on the one cylinder to see if the other will eventually kick in, before stripping the carbs.
Or even priming both float bowls with a syringe and tubing like I believe Dookbob used to do.

jerry · Today, 12:47 PM

Ok checked carbs all in perfect order , so back together and try again ,, well is is sort of running on 2 now but not ticking over even with throttle stop screw wound in and it wont balance up properly its definitely firing better on one than the other ,, one side seems lean but when you change over the HT cables it switches to other side so i will try the electricals from the M750 onto the 750ss to see if it improves ..maybe some component is working but weak ???

I have had it running now for 20 minutes so I reckon the float bowls are full ..

time for a cuppa

Dukedesmo · Today, 01:02 PM

Possible poor connection on one of the pickups/coils etc.?

My bike has an Ignitech ignition module rather than the igniter boxes but, shortly after fitting this I had a cylinder cut out on me. One of the wires in the multiplug on the Ignitech had come loose from it's crimp terminal and so was only making occasional contact.

The odd thing is that the bike sounded and seemed fine at idle speed when running on just the rear cylinder and even on the road it didn't seem particularly rough, just wouldn't go above 40/50 mph.

07-10-2024, 04:52 PM	#1
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,886	Only running on one side 750ss finally running again after 3 years of renovation ,, But only firing on Vertical cylinder ,, Horizontal has spark at plug and coils and ignighters are fine I swopped them around to test ,, there is fuel in carb too but not going bang on that cylinder ?????? Now the carbs have been stripped , Ultrasounded, cleaned and rebuilt with all new seals etc float valve set same on both carbs ,, no leaks or overflowing ? Did it all just like on all my other rebuilds and these carbs have been serviced by me 3 times in last 16 years , so Im not sure now what to do next other than open that carb up again and have a look ???? __________________ MONSTERMAN

Today, 10:38 AM	#3
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,886	OK Swopped plugs , HT cables , coils etc but no change all electicals working correctly nice big sparks ,, but horizontal cylinder still not running just spit backs ,, so it must be carb related .. ho hum .. ???? carbs coming off to check ???? __________________ MONSTERMAN

Today, 12:47 PM	#5
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,886	Ok checked carbs all in perfect order , so back together and try again ,, well is is sort of running on 2 now but not ticking over even with throttle stop screw wound in and it wont balance up properly its definitely firing better on one than the other ,, one side seems lean but when you change over the HT cables it switches to other side so i will try the electricals from the M750 onto the 750ss to see if it improves ..maybe some component is working but weak ??? I have had it running now for 20 minutes so I reckon the float bowls are full .. time for a cuppa __________________ MONSTERMAN

Today, 01:02 PM	#6
Dukedesmo Registered User Join Date: Sep 2010 Location: Leics Bike: M900 Posts: 2,890	Possible poor connection on one of the pickups/coils etc.? My bike has an Ignitech ignition module rather than the igniter boxes but, shortly after fitting this I had a cylinder cut out on me. One of the wires in the multiplug on the Ignitech had come loose from it's crimp terminal and so was only making occasional contact. The odd thing is that the bike sounded and seemed fine at idle speed when running on just the rear cylinder and even on the road it didn't seem particularly rough, just wouldn't go above 40/50 mph. __________________ M900, 916, LeMans II.

07-10-2024, 07:01 PM	#2
Mark64 Bronze Member Join Date: Nov 2014 Location: Hondon de los Frailes Bike: S4r Posts: 292	Electrics is favourite, swap plugs & other components to prove

Today, 12:33 PM	#4
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,558	I know you're very familiar with these engines and their foibles but I can't help wondering how long you have cranked it for and/or left it running on just the one cylinder. My own M750 always take ages to fire up properly on both cylinders after a long lay-off and this seems to be related to the float bowls taking an absolute age to refill after their former contents have evapourated. It is often the case that one cylinder will fire and run for 30 secs to even a full minute (at least it seems like that long) before the second cylinder will kick in. I assume this is while it is trying to fill the float bowls, which seems to take an awfully long time even on the first cylinder to fire and an absolute age on the second cylinder. Of course my fuel pump is original and therefore may not be operating at full efficiency after 25 years of diaphragm deterioration, which may be a contributory factor. Anyway, long story short, it might be worth letting it run for a little longer on the one cylinder to see if the other will eventually kick in, before stripping the carbs. Or even priming both float bowls with a syringe and tubing like I believe Dookbob used to do.