Hesitating throttle and popping noise

[WhiteBeard]

I have a 1985 FJ1100 with a fresh set of carbs installed.

Mikuni 40.0 pilots and 112.5 main jets.
RPM DualPod Uni filters
SuperTrapp 4-1 exhaust with about 10 discs fitted.

What is happening is that the bike seems to run fine on half choke, with nice throttle response.
But when I take it off the choke after the bike warms up, I get very hesitating throttle response and occasionally a loud popping noise from the carburetor area.

Carburetors are brand new so no jets should be clogged. Only thing I know is that the lip on one of the intake manifold rubbers is quite damaged, so might be a leak there.
Could that be causing the issues, or should I be looking into something else?

I will definitely buy a set of new intake rubbers from RPM anyhow, ASAP.

Nat

[WhiteBeard]

Forgot to mention I've synced the carbs and adjusted the idle to spec.
Smoother running now, but problems still persist.

[Dan Filetti]

Sounds like an intake leak.  Testing is easy, spray WD40 or starting fluid eith the mike running (judiciously -no need to start a fire...) around those manifolds see if the revs go up, if they do, you have a vacuum leak.

Dan

[WhiteBeard]

Sounds like an intake leak.  Testing is easy, spray WD40 or starting fluid eith the mike running (judiciously -no need to start a fire...) around those manifolds see if the revs go up, if they do, you have a vacuum leak.

That is good news.
Will see if replacing the rubbers sorts it out.

Thanks Dan!

[Arnie]

Sounds like its starving for fuel.
If you don't have an air leak, I'd richen up those carbs.
You've got a low restriction intake/exhaust with standard fueling.
Raise the needle a half step (0.5mm), and probably open the idle mix screws by 1/2 turn.  You may want to go up a step on the mains as well.

Arnie

[bigbore2]

Did you sort out the problem? What is your altitude there?

[djfrankv]

I have a 1985 FJ1100 with a fresh set of carbs installed.
I swear Im having the same exact symptoms and same exact set up as you on my 84. I solved 80% of the problem by placing small spacers under all four of my needle clips to richen the mix....This helped tremendously.....When I get a chance Im going to add another spacer to the needles to see the problem gets solved. If this doesnt fix it 100%...then I think Im going to have to up my mains. Hope this helped.
Mikuni 40.0 pilots and 112.5 main jets.
RPM DualPod Uni filters
SuperTrapp 4-1 exhaust with about 10 discs fitted.

What is happening is that the bike seems to run fine on half choke, with nice throttle response.
But when I take it off the choke after the bike warms up, I get very hesitating throttle response and occasionally a loud popping noise from the carburetor area.

Carburetors are brand new so no jets should be clogged. Only thing I know is that the lip on one of the intake manifold rubbers is quite damaged, so might be a leak there.
Could that be causing the issues, or should I be looking into something else?

I will definitely buy a set of new intake rubbers from RPM anyhow, ASAP.

Nat

[keand3]

Nat,
Have manage to find out whats causing the issue?

Ken

[WhiteBeard]

Hello guys,

I've been sick for some time now, so haven't been able to find out what the problem is yet.
But my new intake rubbers have arrived on my doorstep, so that is the first thing that gets changed.
BUT, Randy gave me some spacers to shim my needles when he sent me the carburetors. I ignored them since I couldn't figure out what they were for...


Thanks djfrankv, it sounds like this will solve the issue.

bigbore2 - I live at sea level, in a rather cold and humid climate.

By the looks of it, fixing the rubbers and shimming the needles should do the trick.

[WhiteBeard]

Back again...

it's been a very busy time at work, but now I'm finally able to try to fix this problem wholeheartedly.
I have new intake rubbers that I'll install first thing tomorrow morning.

What size washers do I need for shimming the needles?

I'll also be installing a HID kit, Scorpio alarm and a pair of air horns...

Kokalooooooo

[fj11.5]

If they're still in with your needles ,the washers above each one can be used to shim them, ,should be info in the files section if not

[movenon]

Sounds like its starving for fuel.
If you don't have an air leak, I'd richen up those carbs.
You've got a low restriction intake/exhaust with standard fueling.
Raise the needle a half step (0.5mm), and probably open the idle mix screws by 1/2 turn.  You may want to go up a step on the mains as well.

Arnie

Might ad if you think it is a fuel starvation problem. Since you said the carbs were worked on don't overlook the fuel line routing and or a vacuum problem. They are picky about that..... Did you rebuild the carbs ? What I am getting at is there are 2 different needle and seat valves... Probably not it but I will throw it on the table because stuff happens.........
George "adding to the pile"  

[oldktmdude]

   While you're playing with the carbs, check your float heights. Just because they're new carbs doesn't mean that the floats are set correctly. 
                                                                                                                                                                                               Pete.

[WhiteBeard]

Should I use thread lock on the intake manifold screws?
Does anybody know the torque value for them? Can't find anything in Haynes. ..

[WhiteBeard]

Okay, the carbs are back on the bike.

Things done:

• Shimmed the needles (I eventually found that Randy had sent me washers together with some other stuff I ordered... I just hadn't found them.  Thanks once again, Randy!)
  
• Changed all the throttle cables (thanks to Randy...)
• Changed the throttle tube, together with OEM grips (NOS through eBay)
• New intake manifold rubbers (once again, Randy...)

Conclusion:
I haven't had a chance to ride the bike yet, but the throttle response is SOO much better. No hesitation and no pops through the carbs (I think I heard one once, but it didn't come back).
I haven't touched the idle mix screws yet. I might do that next time I have the carbs of the bike.
For now, I'm just waiting to ride...

THANK YOU everybody!

/Nat