VM26SS issues?

[HarlemShake]

I have a 78 GS750C,

I got the bike about 2 months ago. Cleaned the carbs, rebuilt them and it ran like a top!

Took the bike out for my first “long ride” (60+ miles), at about the 40 mile mark the bike started surging and cutting out, popping and back firing.

I limped the bike home via back roads, cause I couldn’t go over 30mph and quarter throttle with a load, it would fall on its face. I can rev the bike with no problems, it’s just under load where I have the issue.

so, I pulled the carbs and cleaned them again. I bought a color tune and tuned the carbs, bench synced them and it ran better, but it’s not zippy. Once the bike warms up it’s popping and surging still.

I replaced the o-rings for the “intake” and there were no cracks in the rubber. I’ve went through and checked timing, valve spacing and all was good.

I’m now confused, only thing I can think is maybe it’s the jetting? I used jets from a rebuild kit. I’m not savvy on carbs and I can’t find anything on the VM26SS. I just want to know what the stock sizes are for all the internals of the carb.

Any other ideas what could be going on? I’m at my wits end.

 

[Nessism]

Did you adjust the valves? Clean & adjust the points?

 

[chuck hahn]

I would supect condensors went bad

 

[chuck hahn]

SERVICE MANUAL HERE........... https://gsarchive.bwringer.com/

PARTS FICHES HERE................ https://www.partsoutlaw.com/

 

[HarlemShake]

Did you adjust the valves? Clean & adjust the points?

Yes, the valves didn’t need adjusting. I did clean and adjust the points.

 

[KiwiAlfa156]

Yes, the valves didn’t need adjusting. I did clean and adjust the points.

By "adjust the points" you mean set the gap? Or do you also mean set the ignition timing using a timing light?

 

[HarlemShake]

I would supect condensors went bad

You may be right, I’ll get some on order and see if that’s the culprit. Considering I changed the coil packs and nothing came of it, that could be it.

I was getting pretty frustrated with everyone telling me it’s the “Carbs”. I’ve gone through those things 5 times in the past 3 weeks.

 

[chuck hahn]

He means setting the gaps AND using usingtiming light to adjustntiming to the F mark. You set the timing on the left ones first with the big plate and the right one last with the subplate

 

[unfocused]

I am going to throw this out there - but where are you floats adjusted at? Even 1mm to high can cause issues - my VM26's I run at 25mm but still tweaking.

 

[HarlemShake]

I am going to throw this out there - but where are you floats adjusted at? Even 1mm to high can cause issues - my VM26's I run at 25mm but still tweaking.

I set them at 25mm as-well. They still need a little adjusting, but I’m not sure that the floats would cause power surges. It literally jolts as if I’ve got power then bogs, then jolts again and back fires. It’s a cycle.

 

[Nessism]

Carbs won't typically cause the bike to cut out when hot. That sounds like an ignition problem or maybe fuel flow, petcock or tank vent problem.

 

[Big T]

But a set of quality points and condensers from a reputable seller.
Don't buy cheap parts from eBay or Temu.

Check your points again, they're probably burnt.

Best solution is a Dyna S ignition

 

[oldGSfan]

Did you stop to fuel up along the way?

 

[HarlemShake]

Did you stop to fuel up along the way?

No, I was on a full tank when I left the house. Fueled the day before.

 

[HarlemShake]

But a set of quality points and condensers from a reputable seller.
Don't buy cheap parts from eBay or Temu.

Check your points again, they're probably burnt.

Best solution is a Dyna S ignition

I ordered condenser and points from a reputable dealer, should be here today. I’m thinking ignition too. It idles fine, it’s under load where it misses.

I’m definitely going to convert to the Dyna S later this summer, just want to make sure the bike is running right before I start making changes.

 

[HarlemShake]

Carbs won't typically cause the bike to cut out when hot. That sounds like an ignition problem or maybe fuel flow, petcock or tank vent problem.

I’m definitely leaning more ignition. I’ve cleaned the tank, I’ll probably coat it soon just to be safe. Vacuum is working well, to the petcock and petcock is clear of any debris. I’ll report back once I have installed the points and condenser.

should have it done tonight or tomorrow. Thank you all for the input!

 

[HarlemShake]

I’m hoping to be able to ride this thing back and forth from Portland and Seattle. Any other upgrades you guys can suggest for more reliability would be greatly appreciated.

its my first bike, and I’m enjoying it a lot. Just don’t want to end up on the side of the road 100miles from home lol.

 

[Grimly]

I’m hoping to be able to ride this thing back and forth from Portland and Seattle. Any other upgrades you guys can suggest for more reliability would be greatly appreciated.

Upgrade the regulator to an SH-775 or equivalent, inspect the stator for crustiness and replace if it's iffy looking.
On a 40 year old bike I'd replace the clutch springs at least, OEM will do, no real need for heavier ones. Check clutch plates for glazing and cracking and replace if necessary.
The above two items are things that will just crop up on you out on the road and leave you stranded out of the blue.
I'd also recommend an inline fuel filter. I wouldn't coat the tank if it's not pinholed - some coatings still on the market react badly to ethanol fuels.
I assume you're already doing the valve clearances, etc.

 

[HarlemShake]

Upgrade the regulator to an SH-775 or equivalent, inspect the stator for crustiness and replace if it's iffy looking.
On a 40 year old bike I'd replace the clutch springs at least, OEM will do, no real need for heavier ones. Check clutch plates for glazing and cracking and replace if necessary.
The above two items are things that will just crop up on you out on the road and leave you stranded out of the blue.
I'd also recommend an inline fuel filter. I wouldn't coat the tank if it's not pinholed - some coatings still on the market react badly to ethanol fuels.
I assume you're already doing the valve clearances, etc.

Awesome and thank you. Yes I’m already doing the valve clearances.

so, I replaced the condensers. The bike is running much better. However, now that I’ve got the color tune on it I can’t get a good air fuel adjustment. So, my jets are too big. I’m having a hell of a time finding the correct rebuild kit for these carbs, as the one I originally got on Amazon came with the wrong stuff.

I’m just trying to return everything back to stock lol. Any help on where I can get the correct carb kit for these would be much appreciated!

 

[chuck hahn]

You dont need kits. Get with Nessism and get a VM ORING KIT. The rebuild tutorials are here

https://gsarchive.bwringer.com/