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switchblade
07-28-2017, 1:45 PM
Does it work the same was as with a car? Are the pressure values/ratios the same as a car? I am bobbing an '82 Yamaha virago 920cc which has some serious running issues and wondering if I can get an idea what's causing the problem by getting a diagnostic engine vacuum gauge but I don't know if the vacuum of a motorcycle engine would register the same on a car vacuum gauge.
Here's some video howtos I was watching on the subject:

https://www.youtube.com/watch?v=utUSI-JYhVU
https://www.youtube.com/watch?v=SdlNwm8OHco

Will it work on my bike?
Thanks.

Tattooo
07-28-2017, 1:59 PM
Does it work the same was as with a car? Are the pressure values/ratios the same as a car? I am bobbing an '82 Yamaha virago 920cc which has some serious running issues and wondering if I can get an idea what's causing the problem by getting a diagnostic engine vacuum gauge but I don't know if the vacuum of a motorcycle engine would register the same on a car vacuum gauge.
Here's some video howtos I was watching on the subject:

https://www.youtube.com/watch?v=utUSI-JYhVU
https://www.youtube.com/watch?v=SdlNwm8OHco

Will it work on my bike?
Thanks.

Plain and simple.... NO Now if your setting up a carb or carbs yes.......

Why not describe what your problem is???

switchblade
07-28-2017, 2:07 PM
Bike sat for 7 years with gas in it. I've cleaned the carbs (3 times now while mis diagnosing other probs) and put new sparkplugs in.
The bike starts fine, idles nicely, any throttle though will try to flood it out and stall.
If I I feather it while adding throttle it won't stall but is VERY gutless (too much gas).
Once I get to 3/4 throttle it seems to even out.
If I open up all the airways to the carbs and add choke it will start and run smoother, until around 3/4 throttle it'll start to caugh and back fire (too much air) unless I then start covering the intake with my hand.
I'm pretty sure my carbs are fine now, it's just something in the system is blocked maybe and throwing off the flow (of gas or air) at certain rpms.
I will be checking the exhaust as there may be dead rodents in there or something. Aparently valves can cause similar behaviour?
Any obvious things I should be checking?

Tattooo
07-28-2017, 2:12 PM
It still sounds like a carb problem to me.... Did you just clean the carbs or rebuild them??? There is a difference....

When the bike is running have you tried spraying starting fluid in the air box when your giving it gas to see if it's starving for gas or is it flooding???

Oh yea you do have the air box back on the bike when your running the bike???

switchblade
07-28-2017, 2:39 PM
Didn't rebuild the carbs, no. I checked around engine briefly for air leaks with starter to see if it would rev. All seemed okay. Air box was on when riding yes. I should have mentioned also, it seemed to run best with carb intake boots back on and vac lines to CV carb diaphrams disconnected from frame. (They connect to 2 tubes on frame which terminate under seat. Kind of odd setup, but it is stock.
You think still carb prob? alright I can check again and blow out all jets. Diaphrams seem to be fine (no holes), need valve seems to lift nicely with air pressure applied, float needs seem to work nicely without sticking etc and it will idle pretty well.
This problem was WAY worse until I realised I had forgotten to put the new plugs in. Once I put new plugs in I was actually able to give it throttle (carefully) and ride it.

Tattooo
07-28-2017, 3:06 PM
Didn't rebuild the carbs, no. I checked around engine briefly for air leaks with starter to see if it would rev. All seemed okay. Air box was on when riding yes. I should have mentioned also, it seemed to run best with carb intake boots back on and vac lines to CV carb diaphrams disconnected from frame. (They connect to 2 tubes on frame which terminate under seat. Kind of odd setup, but it is stock.
You think still carb prob? alright I can check again and blow out all jets. Diaphrams seem to be fine (no holes), need valve seems to lift nicely with air pressure applied, float needs seem to work nicely without sticking etc and it will idle pretty well.
This problem was WAY worse until I realised I had forgotten to put the new plugs in. Once I put new plugs in I was actually able to give it throttle (carefully) and ride it.

I didn't want you to look for an air leak with the starting fluid I was wanting to know if it was running lean...

So with that said,,, Tell you what don't do anything to the bike..... You said you were able to ride it??? Also it's running better??? If that's the case go buy some seafoam at the auto parts store... With a full tank of high test gas put 1/3 of the seafoam and ride the bike... I bet it will fix your problem...

switchblade
07-28-2017, 3:11 PM
Yes I meant to say WHILE spraying for leaks I also sprayed starter fluid in the airbox, reved her up pretty good but I haven't done that since I recleaned the carbs and changed the plugs. Not sure if that will help but worth a try. Tank had some grime in it too so may be still some crap working its way through. Was hoping the vac levels could maybe point out any lingering tourble spots but you say that;s a no go. Thanks for your time man.

Tattooo
07-28-2017, 3:20 PM
Ok now we are getting some where......... Your problem is the trash in the tank....... Everytime you clean your carbs they get trash again right off the bat.....

Take your tank, lines off and carbs again clean them very good or replace them... The lines that is..... Be sure the jets are very clean and you can see light through them and they should look all the same..... The holes are very small and it's hard to get all the sludge out.....

Also be sure when your done get you some seafoam like I suggested.......

Glad to help......

farmall
07-28-2017, 6:20 PM
You can eliminate the fuel tank while cleaning it by running off a dummy tank, such as an old riding mower tank. A dummy tank, some hose, and a shutoff valve (I use plastic Briggs and Stratton inline valves) is very fucking handy.

I use this style on Jap bikes with small diameter fuel lines. https://www.knfilters.com/images/l/81-0221.jpg

When I get a yard sitter I overhaul the carbs (if it's not disassembled and dipped, it ain't clean). Leave the butterflies and linkage undisturbed but remove the slides and jets. Don't just take shit apart. If the black Viton tips on the needles show a smooth line or ridge, replace them.

Inspect needles and seats using a fucking BRIGHT light, and a magnifying glass doesn't hurt either. I've been buying cheap LED headlamps off Amazon for work lights and love them even in a well lit room.

You can leak check carbs off the bike with a dummy tank. I do that outdoors for obvious reasons.

Small inline fuel filters work well, but ensure the hose isn't crimped and all bends are smooth.