Low gauge reading

[walker70]

Hi,have not been here in a while,got my bike out to change the carburetors with a set I cleaned up and put new parts on the inside,put them on and was syncing them up and this is what the gauges are reading,three of them are good but one drops low like it has no vacuum to it,maybe a bad oring at that carb?,I have checked the hoses on the gauges and they look good along with with the adjuster valves,ideas.???

[Maz]

Check the manifold 'O' ring and rubber joint and that the carb top is tight. It may not be the carb at fault. Check compressions on all cylinders. May be a leaky valve or poor ring/bore sealing.
Maz

[DenverWinger]

If I'm reading the gauges correctly three cylinders are reading 5" Hg and the other 13" Hg, so that's high vacuum, not low vacuum. As stated check for vacuum leaks (5" seems a little low on the three cylinders) and proceed with the balance operation, the cylinder reading 13" needs more throttle.

[walker70]

Thanks for the info,but I have used Steve Saunders video for syncing the carbs and it shows the gauges reading like the three on my gauge all across.

[DenverWinger]

That's right, you need to adjust the linkages so the cylinder with the high vacuum reading matches the other three.

[Maz]

Apologies, I read your post and didn't pay much attention to the picture. Denverwinger is spot on with his advice.
Maz

[patbrandon1]

I know you may have already done this step, but...

Did you check that all the gauges are reading the same by hooking each one individually one at a time to the #3 and see if each of them read the same? One of the gauges could be out. Have you used this sync set of gauges before? had you synced the previous carbs?

I believe something is just leaking vacuum, unless the gauges are off.

Good luck and please keep us posted.

[walker70]

Yes,I checked like you say and it is a vacuum leak and I am going to replace all the orings,now I have a question,I have the intake orings but what I am having trouble getting are the ones that go between the plenum and the carbs,dealer says not available thru them anymore,anybody have an idea,I have checked on ebay using the oem part# but no luck,thanks.

[Maz]

Yes,I checked like you say and it is a vacuum leak and I am going to replace all the orings,now I have a question,I have the intake orings but what I am having trouble getting are the ones that go between the plenum and the carbs,dealer says not available thru them anymore,anybody have an idea,I have checked on ebay using the oem part# but no luck,thanks.

Try Randakks, but, as DenverWinger said, that gauge is showing a HIGHER vacuum than the other 3, so opening the throttle plate more on that cylinder (using the sync adjuster) will bring that vacuum reading down to match the other 3.

Maz

[walker70]

Sorry about calling it a low reading,I sometimes get a bit Dyslexic,I know it was reading high,Duh.