- Posts: 53
- Thank you received: 5
'81 750 ltd carb questions
- jason8887
- Topic Author
- Offline
- User
Less
More
12 May 2011 16:13 - 12 May 2011 16:17 #450514
by jason8887
'81 750 ltd carb questions was created by jason8887
I've got an '81 750 ltd (four cylinder) with a 4-1 exhaust (no baffler, actually a cherry bomb on the end of th header... don't ask) with UNI Pod filters and aftermarket coils (can't recall the brand off te top of my head...). Dynojet stage 3 is installed
Bike starts pretty well. After a few seconds of running I start getting a small backfire through the carbs. It is random and is just enough to cause the engine to stumble for a second. That goes away after warm-up. I've already got my air/fuel screws turned out 3 turns. Should I drill the pilots?
Next...
The bike has a soft spot between 1800 and 3000 rpm, like it's getting too much fuel. I have been told the fuel level in the bowl will affect this rpm range. Does that sound right?
Next...
My Keihin carbs seem to have an extra jet in them. I'm used to the main and the pilot but there is a third one in there. Could that be affecting my popping and/or stumble? What rpm range does this jet contribute to?
Finally....
When jetting, do you start with the main or the pilot? I've heard it both ways, but what works on these bikes? It seems like my top end might be a little rich (cherry bomb is black on the inside) but I am tired of doing the dance without some knowledgable input
Thanks in advance
Jason
Bike starts pretty well. After a few seconds of running I start getting a small backfire through the carbs. It is random and is just enough to cause the engine to stumble for a second. That goes away after warm-up. I've already got my air/fuel screws turned out 3 turns. Should I drill the pilots?
Next...
The bike has a soft spot between 1800 and 3000 rpm, like it's getting too much fuel. I have been told the fuel level in the bowl will affect this rpm range. Does that sound right?
Next...
My Keihin carbs seem to have an extra jet in them. I'm used to the main and the pilot but there is a third one in there. Could that be affecting my popping and/or stumble? What rpm range does this jet contribute to?
Finally....
When jetting, do you start with the main or the pilot? I've heard it both ways, but what works on these bikes? It seems like my top end might be a little rich (cherry bomb is black on the inside) but I am tired of doing the dance without some knowledgable input
Thanks in advance
Jason
Last edit: 12 May 2011 16:17 by jason8887.
Please Log in or Create an account to join the conversation.
- kzcafe750_24
- Offline
- User
Less
More
- Posts: 50
- Thank you received: 0
12 May 2011 18:18 #450532
by kzcafe750_24
1981 Kz 750-4 LTD - Wiseco 810 Big Bore,Ported cylinder head, GPZ 750 Cams,Dyna Ignition(DynaS,Green Coils,DRL400 2stage Revlimiter), RC 4 into 1 fitted with Yoshi muffler, ZR550 Swing arm, ZR550 Rear Rim, ZX750turbo front end SuperFlo Dyno Tuned- 68WHP&43WTq(ftlbs)
1986 Honda Rebel 250 (Stock)
1985...
Replied by kzcafe750_24 on topic '81 750 ltd carb questions
That soft spot is affected by the primary jet, that would be the third jet you speak of, should be a #62 if left stock. On my build, I left the pilot jets stock (#35)which affects 0 to 1/8 throttle, then bumped my primary jets to a #65 jet which will affect 1/8 to 1/4 throttle, and then shimmed my needles up equal to one notch which affects 1/4 to 3/4 throttle, and then bumped my secondary main jets up to #135, a little big, but better rich then lean, and this controls 3/4 to WOT. These all blend together in the throttle position, to help with smoothness durning acceration. I just got my bike running great couple days ago, plugs are a nice tan now and she accerates smoothly now, no dead spots anymore.But that's just my bike, every bike is different do to vaccumm in engine, but I'd just keep an eye on the plugs, I probably went through 5 sets of plugs and had taken out the carbs 8 times during my tuning process. But hopefully you can get it figured out.
Good Luck
Good Luck
1981 Kz 750-4 LTD - Wiseco 810 Big Bore,Ported cylinder head, GPZ 750 Cams,Dyna Ignition(DynaS,Green Coils,DRL400 2stage Revlimiter), RC 4 into 1 fitted with Yoshi muffler, ZR550 Swing arm, ZR550 Rear Rim, ZX750turbo front end SuperFlo Dyno Tuned- 68WHP&43WTq(ftlbs)
1986 Honda Rebel 250 (Stock)
1985...
Please Log in or Create an account to join the conversation.
- jason8887
- Topic Author
- Offline
- User
Less
More
- Posts: 53
- Thank you received: 5
19 May 2011 12:13 #452089
by jason8887
Replied by jason8887 on topic '81 750 ltd carb questions
where did you pick your primary jets up at?
Please Log in or Create an account to join the conversation.
- kzcafe750_24
- Offline
- User
Less
More
- Posts: 50
- Thank you received: 0
23 Jun 2011 03:43 #458854
by kzcafe750_24
1981 Kz 750-4 LTD - Wiseco 810 Big Bore,Ported cylinder head, GPZ 750 Cams,Dyna Ignition(DynaS,Green Coils,DRL400 2stage Revlimiter), RC 4 into 1 fitted with Yoshi muffler, ZR550 Swing arm, ZR550 Rear Rim, ZX750turbo front end SuperFlo Dyno Tuned- 68WHP&43WTq(ftlbs)
1986 Honda Rebel 250 (Stock)
1985...
Replied by kzcafe750_24 on topic '81 750 ltd carb questions
Oh, really sorry for the very late reply. Site never sent me a message that you replied back.
But I pick my jet at www.jetsrus.com , you probably got a different place by now.
Sorry about that jason8887.
But I pick my jet at www.jetsrus.com , you probably got a different place by now.
Sorry about that jason8887.
1981 Kz 750-4 LTD - Wiseco 810 Big Bore,Ported cylinder head, GPZ 750 Cams,Dyna Ignition(DynaS,Green Coils,DRL400 2stage Revlimiter), RC 4 into 1 fitted with Yoshi muffler, ZR550 Swing arm, ZR550 Rear Rim, ZX750turbo front end SuperFlo Dyno Tuned- 68WHP&43WTq(ftlbs)
1986 Honda Rebel 250 (Stock)
1985...
Please Log in or Create an account to join the conversation.