1980 Maxim 650 Throttle lag

Hi Everyone !

I picked up my Maxim in the spring and have been working on its since I got back in the summer.
I am having issues with the throttle lagging, after I give it gas the RPMs go up fast and smooth however when I release the throttle the RPMs drop pretty darn slow.

I have cleaned and rebuilt the carburetor (didn't take apart the 4 carbs, just cleaned all passages and internals since I was worried about calibration issues).
I have tried disconnecting the throttle cable and manually opening the spring loaded throttle(no difference ) so I ruled out friction in the cable and the housing.
I have tried removing the air filter to see if it was too clogged up, no difference again.
The only next step that I can try that I know of from looking at some of the posts on this forum is to check intake and exhaust valve clearances however I'm not sure if that is even relevant however.

I have an inkling its something small and silly I'm missing so any advice or ideas are greatly appreciated.
(Lastly not actually sure what its exact model name is or where to find it on the bike. year is for sure 1980. so I suspect XJ650 G Maxim 653 cc)

 

Check for vacuum leaks. If you did not break the rack then the carbs are not clean and very good chance the throttle shaft seals are hard and cracked as well. Do yourself a favor and order parts from chacal (xj4ever,top right corner of page) and take those carbs to church

 

Absolute must.......full teardown of those carbs...break that rack & do it right......replace the throttle shaft seals ( 8 of them ...2 each carb ) and replace the o-rings for the fuel line between carbs.....

Take your time....work methodical.....& do it once.....the right away......

But also sounds like you may have vacuum leaks........r all of your boots in good condition......( intake manifold & airbox boots )...

 

are the clamps all tight and seated properly?

 

I will pull out the carbs and have a go at breaking them up.
Boots are in good condition, so I expect that is most likely not the issue.

side note if I turn the idle screw out then the throttle becomes responsive however doesn't idle any more. Does this help in narrowing down the problem?

 

do you mean the O clamps between the carbs- air filter box and carb- engine?
if so i will give them a look over, but I believe I have already seated them correctly.

 

yes could be a sorce of air leak.

could be you just need to sync the carbs. sounds like it was turned up to far

 

Are you talking about the 4 screws on top near front of carbs ( mixture screws)or the 1 idle knob under carbs to set idle?

 

Throttle shaft seals?

 

where are these.....those are not out of carbs ???

 

Yes they are..... They are throttle shaft seals, mixture screw plugs., and fuel supply o-rings..... Etc.....

 

Do you know if the throttle shaft seals & fuel o-rings were ever replaced ??? Just curious ....

 

Maybe it is the closeness of photo that fooled me......oops

 

what are the brass ones??? Forget it.....mixture plug screws....I cant read today

 

brass ones ? where is matti when you need him

 

Just playing with the main idle knob in the center under the carbs.
Havent touched the 4 screws yet.

 

so after some time in I have gotten it working well, I was not giving the bike long enough to warm up before setting idle adjustments which was the main source of error .
Thanks everyone for the advice!