Specific carb question

82 maxim 750. Question relates to one specific area of the carbs.

1). The jet that is deep in the side of the float bowl. Manual calls it the starter jet.
2). The small tube that sits on or near that jet when the bowl is installed.

Question is- if either is obstructed, what are the symptoms when the bike is ridden?

 

No symptoms when the bike is operated without any choke being applied. Clogged starter system manifests itself only when the choke is used (cold starts) when it fails to start (because the starter or, more properly, the ENRICHMENT CIRCUIT is clogged.

 

Hard starting when cold and no fast idle when cold.

 

Would be best to clear that jet and brass tube out all the way up to the plungers.
It will be very cold blooded and would be hard to get going on a cold morning.

 

Hmmm. Not what I was hoping for. Let me explain symptoms. Bike starts first try with EC used. Settles into nice idle as it warms. Disengage EC. Try to pull away and bike starts to move but as rpms increase bike stumbles, threatens to stall. Give it more gas and when bike reaches about 3000 rpm it takes off like a scared rabbit. Or, leave the EC slightly engaged and problem goes away but idle is uncomfortably high. If sitting still, bike will take gas no problem through entire range. If cruising at steady throttle and rpms are in the 2000-3000 range, bike misses and stumbles but gas it and it goes great. So, long story short, what part of these carbs handles the transition from idle jet to main jet.

 

the needle jet and the needle jet needle. if this is a stock bike and has stock jets, open the idle mixture screws 1/8 turn and try it. 2.75 turns out from bottom is a good starting point if you want to go from scratch.

 

Sorry, Polock, I am terminolgy challenged. Are these what I would call the 4 mixture screws on the top of the carb? If so, I have them set at 2 1/2 turns out. So I am running too lean? Can it really be that simple? Please let it be so!

 

Or, it sounds like the EC is clear, but the pilot fuel circuit is compromised (clogged on pilot mixture screw very badly adjusted).

Of course, the engine may just need a good synch.

 

that's them. now this takes for granted that the carbs are clean and the jets are stock, no pods, no open pipes.
the slides in the carbs work smoothly, the diaphragms don't have any holes and are seated right. the holes in the needle jet are clear and no shims under the needle.
set those screws to 2.75 and do a running sync. then see what you have

 

..... And that's with the valve clearances back in spec......

 

I hate this iPad!!! Keeps wiping me out.

Pure stock, synched, valve adjusted, rebuilt EC with parts from Chacal. Fuel and air jets clear, starter jet clear, slides good and clunk. But, that said, Chacal has me worried with "if pilot fuel circuit is compromised". That would be a problem as I wouldn't know what comprises that circuit. I pulled the mixture screws and sprayed with cleaner. Will re-adjust mixture in am.

 

compromised would be a clogged jet or passage or something on the idle(pilot) jet screw slipped or in the wrong order.
the adjustment screws should have a spring then washer then o-ring, in that order. the o-ring can slip when installed or maybe the old one wasn't taken out. sometimes people clean jets too aggressively and change the size

 

those tiny o-rings have been smashed for 30+ years get new ones

 

Replaced. Thanks all. Will let you know.

 

The pilot system is the primary source of fuel at idle and up to approx 1/4 throttle, so I'm with Chacal that you have a problem there. I would remove the carbs and make sure that system is absolutely clean and clear and check that the little 0-rings are good. Assuming the valves are set and the carbs are sync'ed, then use a colortune plug to set the pilot screws. I suggest starting at a lean setting and opening the pilot screws until you get a blue flame and then install new plugs, (new plugs makes reading them much easier) take a ride and look at the plugs. Then adjust the pilot screws--about the thickness of a dime-- and ride again and read the plugs. Do this until you get the plug color good and you should be in good shape. At least that's how I got my bike running well.

 

Not to be difficult but please define what comprises the pilot system and how to clean it. I removed the screws, used new orings and washers from Chacal, blew cleaner into the opening as best I could. What else can be done?

 

Pilot circuit-sometimes called "idle" circuit....also includes enricher circuit for cold starting.

Brass tube on bottom of carb extends into the small deep well in the bowl. Tiny fixed jet at bottom of bowl.fuel is drawn through enricher plunger and also mixture screw. ALL THAT MUST BE SPOTLESSLY CLEAN. Idle jet, next to main (primary jet) leads to small holes above the butterfly, etc.... Passages must be spotlessly cleaned. Primary is what you run mostly on, other do still contribute. All must be impeccably clean.

But, here's a question---- are the valve clearances in spec?

If you think carbs still have issues, I offer carb rebuild services.... Contact me.

Dave F.

 

Airhead Valve Adjustment

Carb Cleaning; The whole 9 yards.

The Church of Clean

The Secret Life of Carburetors

 

Thanks. Started a conversation with you.

 

Got it, replied....
Here's another question--- did you do throttle shaft seals and/or fuel rail o - rings?

 

I have the same symptoms, and will follow this thread. I plan a full carb rebuild over the Winter (and perhaps a brake line change). Let us know how you make out.

 

Valves should be fine. Adjusted a few years ago but very few miles since then. Bike always ran perfectly until the bike set for a year due to health issue. Have never touched shaft seals or o rings.

Now, chapter two of this miserable saga.

Before going on a 30-40 mile ride with my son yesterday (81 SECA 750) I opened up the mixture screws 1/2 turn just to see what would happen. Well, three things happened.

1) bike became hard to start. Seemed to flood immediately but eventually started.
2) the symptom I have been fighting went away. Bike pulled away great, ran perfectly at all throttle settings. Set off on our ride.
3) after about 20-30 miles we stopped to get a cold drink. Leaving there, the symptom returned, just as before. Very depressing to say the least. Defies logic.

 

Throttle shaft seals have an age limit. Throttle shaft seal failure will cause the symptoms you are experiencing.

 

I will check them with carb cleaner at idle and see what happens.

 

1/8 on top of the 1/2 or 1/8 from the original setting? Would guess the latter.

 

1/8 from the original setting, what it seems like you did was go from slightly lean to very rich. never adjust more than 1/8 turn at a time

 

Good advice. While I am here, a couple related thoughts. Firstly, it would appear that that setting is very sensitive. What about setting to 2 1/2 and increasing 1/8 at a time? Lot of busy work since tank has to moved. Also, the one part of these carbs that I can't swear is really truly clean is that venturi tube that goes into the float bowl. I can tell you the starter jets were very plugged. But many have said no impact on my problem. Does the fact that the bike started well mean the tunes had to be clean?

 

Are the transition jets clean? They are the two other holes (near the idle screw pintle) that are behind the butterflies. They play a huge role during off - idle conditions, right before the needle jet starts to lift.

 

Hmm. Not sure. Wish someone had illustrations with terminology for all of these ports,tubes,jets,passages,etc. Manual sure is lacking for anything but the big components.But wouldn't those be air jets?

 

Not air jets. They are part of the pilot fuel circuit. Before the fuel of the pilot fuel circuit goes into the carb's throat, fuel will come out 3 different ports. One is where the idle fuel screw's point meters fuel for idle speeds. The other two holes get uncovered when the throttle butterfly plates rotate and vacuum pulls out fuel from. Basically, these are your 'cruise' or transition jets.

 

See pages 18-20:

http://www.xj4ever.com/inside your carbs.pdf