Yamaha Starbike Forum banner
  • Hey everyone! Enter your ride HERE to be a part of this month's Bike of the Month Challenge!

21 - 40 of 43 Posts

·
Registered
Joined
·
55 Posts
Discussion Starter · #21 ·
Do you have a way to test fuel pressure?
Have you tried bypassing the fuel pump?
Doubtful that you have 4 defective neddle/seats, l could see one but not all 4.
I dont have a way to test fuel pressure. But what i did on both pumps was took my finger and plugged the end of hose that connects to the fuel rail on carbs, i turned the key and switch on and they both clicked 2 or 3 times before it stopped. Also, both fuel pumps click the same amount of times after i reinstalled thw carbs on the bike ans when thw bike is running they click the same.
This leads me to believe the pumps are fine and its a carb issue. Both pumps are a 2 to 4 psi.

Bike was running just fine the other day i had no issues after setting pms screws and carb syncing and then all of a sudden i went to lunch, went to start my bike and it stopped which meant i almost hydrolocked my motor. Hit the starter again, it started but ran differently as in when i got home i took tank and airbox off to see the excess fuel was coming out of the main jets/needle jets flooding 3 of the carbs.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #22 ·
Thats when i did the compression check ams 3 cylinders were 185 and one was 178 so i didnt bend a valve and from what i was told is the compression is good and a starter can not bend a valve.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #23 ·
One last piece of info is after reinstalled carbs, start the bike it runs good and after about a min maybe less is when fuel starts coming out of the main jets/needle jets. So it doesnt happen right away.
 

·
Registered
99 Roadie
Joined
·
677 Posts
Did the orings around the needle seats get chipped during installation?
I've had that happen to me a couple of times.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #25 ·
Negative. I inspect needles and seats with a magnifying glass, still wouldn't explain why i dont leak air when pressure testing the fuel passages.
 

·
Registered
99 Roadie
Joined
·
677 Posts
All 4 should be jetted the same.

The fact that it takes a few minutes to start flooding tells me this is a very small slow leak.

It's hard to find tiny leaks with air unless you have some way of measuring pressure decay.

Have you tried putting fuel to the carbs upside down with the bowls off.
Liquid (fuel) will allow you to see the tiniest of leaks.

The needle/seat assemble or the o ring around it where it installs in the carb body are the only place where fuel gets in the carbs.

Maybe take them to a shop and have a tech look at them.

Just out of curiosity what size are the float needle seats, and what brand are they?

Also main or pilot jets have nothing to do with this.

This is strictly a delivery issue.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #28 ·
All 4 should be jetted the same.

The fact that it takes a few minutes to start flooding tells me this is a very small slow leak.

It's hard to find tiny leaks with air unless you have some way of measuring pressure decay.

Have you tried putting fuel to the carbs upside down with the bowls off.
Liquid (fuel) will allow you to see the tiniest of leaks.

The needle/seat assemble or the o ring around it where it installs in the carb body are the only place where fuel gets in the carbs.

Maybe take them to a shop and have a tech look at them.

Just out of curiosity what size are the float needle seats, and what brand are they?

Also main or pilot jets have nothing to do with this.

This is strictly a delivery issue.
Just got a different rebuild kit from dennis kirk. Ive never had an issue buying anything from dennis kirk.
Parts unlimited i guess is the brand.
Stock 95 main jet and stock 20 pilot jet are in it.
16232825616074099798541549042281.jpg
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #29 ·
I dont understand why it says closed course racing only on it.

Original untouched carbs had stock 20 and 95 in them?

I have them all apart and am going through every passage with a tiny copper wire, carb cleaner and compressed air. Are there any orifices that could also cause my issue?
16232828350614435114452695322405.jpg
1623282860915116025285362955037.jpg
 

Attachments

·
Registered
99 Roadie
Joined
·
677 Posts
As long as all of the atmospheric vents are open that part of the job should be fine. The cause of
fuel getting by the needle valve assembly probably isn't due to plugged vents.
Check the vent lines that connect to the carbs as well.
A fuel tank that doesn't vent properly can cause issues like yours.
 

·
Registered
Joined
·
9 Posts
The o-ring around the needle seat can leak causing flooding.
Plugged pilot or main jets will not cause flooding, they will cause a lean condition.

Once you have set the float heights position the carbs upright as they would sit on the engine and with a remote tank of some sort apply fuel to them.
Let them sit for a few minutes and see if they leak fuel. If they do then the needles for some teason aren't shuuting off fuel when the bowls are at the correct level.

Blocked atmospheric vents will cause poor fuel level control and cause the bike to run poorly.

Are you sure it's flooding?
Are the plugs excessively wet with fuel or do you see black smoke at the exhaust pipes?
The simplest answer is probably the right one.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #32 ·
Preliminary results show that my problem is solved with the umpteenth carb breakdown, cleaning, and new rebuild kit. After careful inspection of all parts, i assume the new needle seats i previously installed had an o-ring defect in the diameter itself to where it apparently was allowing fuel to overflow the carbs and come out pilot and main jets. I set the floats a little above 9 mm as these ones i had not touched and their height was between 10.84 and 12 ish because i spent 6 hours on doing this with a break to eat dinner and i will fine tune them tomorrow after work as i expect to be lacking in my higher end speed and acceleration in the higher gears and rpms. I will also be readjusting the pm screws and syncing the carbs. I have drained the oil and leaving it open overnight as to allow the majority of oil to drain and the rest of the gas in the oil to evaporate.

I appreciate the words of wisdom and hope that when i button everything back up that all will be well.

Troubleshooting this ordeal has been exhausting and as sure as carburetors will be around for a while longer, maybe some other poor fool like me can get the help they need.
 

·
Registered
99 Roadie
Joined
·
677 Posts
Glad you found the issue.
The kit says "closed course use only" to get past DOT certification requirements.

The companies that sell the kits source thier components from different suppliers so quality can be hit and miss, sometimes things say they fit but really don't.

Keep us posted on your progress.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #34 ·
Rode the bike to work today and it sputters with anything other than slight acceleration. You can hear the difference between the left side and right side exhaust. Left side is strong amd steady and right side not so much and its acting lean possibly like a cylinder isn't firing correctly. If you WOT in any gear it sputters and then clears up back amd forth between the two. So its like it sputters for a brief second and then clears up and repeats every second while WOT.

Not sure if its a spark plug bad(they are oem NGK's bought 3 weeks ago) or somehow my TPS got messed up even though i never loosened it ever.
Just bums me out, bike was great, almost had a hydrolock and now i still have trouble although my excess fuel out the main jets seems to have been remedied.

After work ill check the spark plugs on the right side of bike and go from there.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #35 ·
It never sputtered like this before not even before i just installed the rebuild kit and the excess fuel issue. Any ideas what i possibly did? The floats as mentioned were high tens to almoast 12 ish when bench setting them and now they are 9.2? Higher number is less fuel so now i know that that the fuel level is more ans closer to what it should be.
 

·
Registered
99 Roadie
Joined
·
677 Posts
Been my experience that ngk plugs that get fouled a couple of times won't run right even if they look good.

On the fast bikes l work on I've found that a millimeter of float can make a big difference.

Don't give up👍👍
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #37 ·
Been my experience that ngk plugs that get fouled a couple of times won't run right even if they look good.

On the fast bikes l work on I've found that a millimeter of float can make a big difference.

Don't give up👍👍
I thought i had an intake leak turns out i dont.
Like i said it sputters/bogs down with any throttle above a hair. I rode it like a raped ape today and i noticed that reaching the end of the rpms in first, second, third and fourth the sputtering got worse but also cleared up at the same time and when it briefly kicked in the exhaust sounded almost normal,pre carb rebuild.

I have a theory that because my needles were leaking it compensated for the low float height (10.5 to 12mm) and ran pretty decent. Now, that needles and seats are fixed, the incorrect float level, is causing the sputtering, bogging with any throttle? Is this possible?
I pulles the plugs one by one while it was running and they all affected the idle(drop in rpms) i looked for intake leak below carbs and thought i had one and i slightly did but did not remedy my issue. Problem seems to be mainly on right bank of carbs because i still hear popping from right exhaust pipe but both pop pretty loud when i blip the throttle above halfway.
Have you or anyone had an issue with incorrect float heights causing my problem after a carb rebuild?
 

·
Registered
99 Roadie
Joined
·
677 Posts
Float height determines the amount of fuel in the bowl. The more fuel in the bowl, the deeper the jets sit in the fuel increasing what is known as "head pressure" causing a richer mixture.

Too low of a fuel level in the bowl makes it leaner.

Usually breaking up under load is from a lean condition.

In some cases, especially with semi-downdraft carbs, too high of a float level (low fuel level in the bowl) setting will cause the float to touch somewhere in the bowl and not open fully.
This will restrict fuel flow and the bowl will run dry under heavy throttle. This is rare but I've encountered it and it's difficult to diagnose.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #39 ·
Float height determines the amount of fuel in the bowl. The more fuel in the bowl, the deeper the jets sit in the fuel increasing what is known as "head pressure" causing a richer mixture.

Too low of a fuel level in the bowl makes it leaner.

Usually breaking up under load is from a lean condition.

In some cases, especially with semi-downdraft carbs, too high of a float level (low fuel level in the bowl) setting will cause the float to touch somewhere in the bowl and not open fully.
This will restrict fuel flow and the bowl will run dry under heavy throttle. This is rare but I've encountered it and it's difficult to diagnose.
[/QUOTE

I read somewhere that if i start it and let it idle for a min, give it throttle while pulling the choke to determine if its lean or rich. I did so and the choke had no effect when opening up the throttle it still acted the same. Without throttle and the choke pulled out it rose the rpms.
I pulled the plugs and these are the result of riding it about 20 miles with the condition its in.
Attached are photos of the plugs.
All were dry. Im no good at reading plugs.
Thoughts?
20210611_061653.jpg
20210611_061634.jpg
20210611_061559.jpg
20210611_061537.jpg
 
21 - 40 of 43 Posts
Top