Idles well, no throttle response

I have a weird problem going on that I can only assume is carb related or maybe electrical ignition. I got this bike with the carbs already pulled off and somewhat disassembled . I finished going through them and thoroughly cleaned all the bowls , jets, needles/diaphrams, and cleaned and lubed all the assemiles on the outside. All slides worked great with nice vacuum chugs and had controlled return down. Jets were soaked and are clear, along with passages in carb.

So here's the dilemma. The motorcycle will start and idle great, for long periods of time even , but does not Rev at all with throttle. And I don't mean it bogs down, it just doesn't respond at all even with full throttle. Stays at the same idle and exhaust note subtlety changes but no rpm increase or anything. Throttle cable moves, pulls up on the carbs and moves all the linkages, but nothing.... It's very strange. It seems mechanical to me, the butterfly opens, needle goes up, more gas goes in, the engine revs. Not sure what I'm missing.
Inspected the petcock. On reserve it flows with vacuum, on primary it flows freely vacuum or no vacuum, and doesn't flow when at the on position. Kinda weird but by having it on primary I know it's not a fuel starvation thing. I can also see the lines filling up via my clear gas filter. Any thoughts on where to point me? I was very thorough with the carbs before reassembly. Everything cleaned out etc and double checked everything but I could maybe run through them again

 

Bryce, put your bike specs in your signature so we know what you're dealing with... That does sound weird. Has anyone here ever have a finicky TCI that created this sort of problem?

 

Is the factory air filter box installed and all the connectors to the carbs? Or POD filters?
If you have carbs on with nothing on the inlet side of them the engine won't respond to throttle. It will just spit and sputter.

 

^^^+1 agree sounds strange.

 

Don't think it electrical..sounds like it is carb problem are all the jets in CORRECT position?

 

connected the throttle cable to enrichment circuit/choke vice versa ? spose you would feel the diference on the throttle ..one or two diaphrams unseated wedged between lids ? i had one this way caused starting problems not sure what else it would cause but it might stop slides going up properly

 

Sorry it's a maxim 750. Stock air box with a brand new uni filter. I guess it's possible I switched jets but not super likely. Bigger ones on the larger more centrally located threaded post yeah? Smaller jets went to the shorter post? Other thing to note. Warning light is flashing. These bikes do not have a limp mode or ignition retarding do they?

 

Throttle cable is the link in the middle right? Choke hookup is on the right side of the bike and moves the four little needle like things simultaneously? If so I have that correct as well

 

are all the exhaust pipes getting hot?

 

I wrapped my filter frame with UNI foam and it did run leaner. Can you turn the idle knob and get more rpm?

 

To Group:

Warning light? Is there a separate indicator on a 750? My 700 only has L&R turn indicators, Hi Beam, Oil, Low Fuel Indicator & of course Neutral.

What might trigger a warning light to flash?

 

The LCD should tell you why the warning light is flashing, bulb burned out, battery fluid level low, low fuel level, etc. I believe only the early 750's and and 1100's had the Atari with the annoying flashing red warning light. The light does not affect the engine running.

 

Did you inspect the slide diaphragms for pinholes?
Did you make sure that all of the air passages and jets are clear?

 

No limp mode. The systems monitor is not tied to the ignition at all.
As mentioned the LCD will tell which system has a fault. The light is just to get your attention. If you press the reset button it will sotp flashing temporarily.
The most likely cause is the battery monotor not being hooked up to anything.
Most people toss the sensor with the old battery, and don't know that you can get a new one, or that it an be turned into a voltage monitor.
The wire is white with a red trace, and can be found near the positive battery terminal.

 

You sir are into something. After a minute or two of idling the left header is piping hot, the 2nd one from the left is warm, and cylinder 3 and 4 are cool to the touch. What are the implications of this? Also when cranking I had spark to all 4 cylinders if that helps understand what's going on and eliminate some things with this

 

Thanks for The suggestion. I have already put an inline resistor and turned that into a voltage reader. I'll check what the warning is for and fix it eventually but I'd like to get it running and then track down little things as I go

 

The implications are plugged pilot passages on those carbs.
When you cleaned the carbs, did you fully disassemble them, remocing all rubber parts (including the pilot mixture screws and their o-rings) and dip the carb bodies?

 

I went through them pretty well. Fully dissasembled and pulled the Jets etc. Jets are definitely clear, held them up to the light after cleaning and compressed air blown through to make sure they were clear. diaphragms were good, i feel like i remember shooting carb cleaner down the passages for the Jets and seeing the stream shoot out the outlets. It will be miserable but maybe I can pull them again and reinspect/clean. Won't have time till the weekend but I will try that and follow up again.

 

But did you pull the idle mixture screws?

You have spark.
You do not have fire at idle.
Therefore the idle passages are plugged.

The only other possibility is that you have deadly-low compression on those cylinders, or a big vacuum leak(s).

 

Did you check and adjust valves..WILL need done. One other possible thing un screw the plug caps snip a 1/4 inch off end rethread on and see if cylinders kick in.

 

you also have to spray cleaner down the air jet under the diapram with your thumb over the mixture screw hole, then seat the mixture screw in lightly and repete
you could have a clog between the outlets and screw put your finger over the outlets in the carb throat

 

it is a quick method to tell if all cylinders are firing then you have to figure out why they are not firing,
a.no spark
b. no fuel
c. valve train problems
d. compression problems
list goes on

 

Thanks for the input so far guys. What a great active forum. Looks like i have a few places to start this weekend.

Odd occurrence tonight, started it up and it revved to 4k rpm and stayed there. Turned it off almost immediately since that is no good for the bike. Scared the heck out of me. I started it 2 or 3 more times later and same thing. Pulling the throttle cable changed nothing. Then I started it a half hour later and it was back to an idle around 1500. Pulled the choke outta curiosity, went up to 2k rpm and after closing the choke rpms wouldn't drop back down. 1st header and 4th header were now very hot and 2nd and 3rd still cool To the touch. Hmmm

 

someone mentioned vacuum leaks its always bit of a problem when taking carbies off and putting them back on can split rubber intake boots or get the airbox boots squished outside of sight perhaps even the vaccuum line end is warn and sucking air and not pumping fuel fast enough

 

4K is not bad for the bike, it just isn't correct when it happens as you described.

When you get things sorted out (and you will), you will find out that Happy begins above 6k.

 

Still getting used to that myself...

 

have you ohmed out the ignition system yet you should do that I have a post in this thread
Gonna get more carb removal and install experience

 

haha im selling mine pay off my credit card besides i got nowhere to ride too an im tired of taking the carbies off lol

 

Got this sorted out this weekend for anyone interested. Took the carbs off and went through them again. The first time through I missed the air jets that are under the diaphragm for the pilot and main fuel. A main jet one was clogged, others were OK. It must've been late at night when I put these back together because there is a chance the floats were maybe installed upside down.... And the one I got parts for and finished later was installed in the opposite direction. I'm guessing that was the cylinder that was working and the other 3 weren't. Im still not sure it was the floats as I didn't pay attention on disassembly as well, I just made sure I put them back right. So for anyone with the same problem, check your air jets hidden under the metal cover just under the diaphragm and clean out the passages for them as well. Bike is finally running for the first time in 8 Years! Now just to get those brakes bled and I can start a thread showing the complete rebuild

 

Plugged air jets....hmmmmm.
I'm glad that it was something simple.

 

lol brakes bled dont bother buy a new master cylinder repair kit a piston seal kit and new brake lines it will save you time in the long run