Bogs down above 3500-4000 rpm

[Atlas]

Hi and good afternoon , I have an issue with my 1980 GS750 , here's a little back ground. This bike has been sitting indoors more than 20 years with gas in the tank , which obviously gummed up the carbs and the fuel tank was a mess. When I pulled them apart the problem was all bottom end related where the gas sat in the fuel bowls. I thoroughly cleaned and rebuilt the lower end of the carbs. The only thing I didn't do was remove the needle jet tubes. I know ,I know , thats dumb , but when I did the tear down , that area all seemed clean. The slide and jet needle appeared to be clean except right at the bottom, where the main jet sat in the fuel. I've already given myself all of the finger wagging and "you dummy you shoulda" stuff, so be nice and spare me that:lol: What I need from you , "the experts" is a little advice and know-how.

My question is ; if the engine bogs above 3500-4000 rpm , could this be an indication that the needle jet tubes are plugged and fouled up? It seems to be a higher rpm issue and I'm wondering if the little side holes are plugged on the tubes. If I try to accelerate and it bogs , if I pull the choke it will take off temporarily with that extra shot of fuel . It starts great and once warmed up idles quite well and doesn't stall out unless it drops below 750 rpm. The engine runs great and is quiet with no noises. All of the tank/petcock fuel delivery stuff has been addressed and taken care of , the fuel bowls all have fuel in them. I've also replaced the plugs. Other than the carbs this bike was in good condition and was well maintained when it was used , everything is still functioning well even the fuel gauge. Any help would be appreciated , Dave

 

[Nessism]

Is the bike stock or modified? Airbox in place and sealed?

 

[Atlas]

This bike is totally stock , the airbox is not in place

 

[Guest]

Clean the carbs properly and put the airbox on.
The bike will not run right without the box installed or with clogged needle jets.

 

[Nessism]

Read this...particularly #4 http://www.thegsresources.com/_forum/showthread.php?t=171846

 

[Atlas]

Well the easy part is to put the box on and try that first. I take it from your response that it could very well be the needle jets , and that this problem is indicative of fouled needle jets .

 

[Atlas]

Read this...particularly #4 http://www.thegsresources.com/_forum/showthread.php?t=171846

I'll get right on that, I didn't realize that it could make such a difference. Thanks, why would that make the engine bog

 

[Guest]

I'll get right on that, I didn't realize that it could make such a difference. Thanks, why would that make the engine bog

with out the air box it gets to much air and not enough fuel, on that bike even the filter cover off or the seal missed up will make the bike bog

 

[Guest]

with out the air box it gets to much air and not enough fuel, on that bike even the filter cover off or the seal missed up will make the bike bog

I just had a 80 750 L that I did a proper carb cleaning total strip and dip , new o-rings , and intake mounts. When finnished bike would bog, about 3500rpm , further investigation revealed that the gasket on the filter cover was bad put new gasket in bike ran fine no more bogging

 

[Atlas]

I just had a 80 750 L that I did a proper carb cleaning total strip and dip , new o-rings , and intake mounts. When finnished bike would bog, about 3500rpm , further investigation revealed that the gasket on the filter cover was bad put new gasket in bike ran fine no more bogging

I'm going to try that first before I pull the carbs again for sure. I'll definitely let you know if this was the culprit. Thanks

 

[Atlas]

Well, I thank all of the respondents to my question , I'm happy to report that the bike is running awesome. I'm very grateful for the advice, you saved me a lot of time. I was about to pull the carbs off again and check the needle jets because of you I can now watch the Canucks/ San Jose hockey game. I'm amazed that the breather box would make that much difference , but it does make sense .