Question about tuning engine

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Jack Lagachette

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ok, i try to tune my engine and now my engine is very unstable , sometime on the idle he run high , then after a few high speed pass , he run low .. and finally stop , i try the high speed , the low speed needle :confused: , im so bad !! lol ! or sometime on the idle .. the RPM go up.. then down .. then very up .. and down .. and die ..


ps : i make the tank vent mod .. so its not the problem ..


so if anybody can help .. i appreciate .. one day , i be good .. lol !


thx guys
 
Jack Lagachette said:
ok, i try to tune my engine and now my engine is very unstable , sometime on the idle he run high , then after a few high speed pass , he run low .. and finally stop , i try the high speed , the low speed needle :confused: , im so bad !! lol ! or sometime on the idle .. the RPM go up.. then down .. then very up .. and down .. and die .. ps : i make the tank vent mod .. so its not the problem ..

so if anybody can help .. i appreciate .. one day , i be good .. lol !

thx guys
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I had the exact problem with one of my stock carbs. Some of my Cats never had this issue, but the carb on my MT did. This issue can also be caused by an air leak behind the carb.
 
might not be the leak you think it is ....I've had a tiny bit of 'dirt catch' oil around the throttle rod but that wasn't the problem....you just might have an isolator block screw loose or carb screw loose.
 
+1 my carb was loose. I didn't find out until I started disasembling for the new 990. No biggy as I wanted the 990 anyways.

The plastic manifold between the carb and engine can warp causing a leak also.
 
I too would suspect an air leak. Best thing to do would be pull the motor and replace all gaskets, I know it's alot of work but it's cheap compared to replacing the motor.

I know some may disagree, but the 813 in the hands of an experienced tuner is an awesome carb! My Marder fires on the first pull, idles like a dream, holds a tune and snaps out of the hole without even a slight bog.

Lets hope this carb will do the same on my XB when it gets here.
 
Yep, air leak. Make sure the carb and intake bolts are tight. The 990 is a great carb, I love mine!

I don't use the 813 because I don't want to have to constantly replace the throttle shaft.
 
i agreed stock sucks my car ran beautiful with that 990 carb before i crashed it, but a word of advice instead of trying to pull start it ten times put your hand over the air filer assy so you cant "choke" it so it starts immediatly. Also i noticed walboro sent me the carb with too lean of a setting, so when you get the carb go ahead and reset the screws to your liking.
 
+1

Carbs don't necessarily come preset. I never even try to start it with a new carb with out checking the needles first.
 
Deluge said:
I don't use the 813 because I don't want to have to constantly replace the throttle shaft.
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I have well over 20 gallons on the same GP290 and 813, no shaft issues for me...

It's unfortunate that a few inexperienced tuners had carb issues, now the 813's reputation is in the shitter... The 813 is by far the best carb I have ever played with. I am a small engine mechanic by trade and I still will vouch on the behalf of the 813. I will fault the tuner 10 times over before I fault the carb.

In the right hands, (In my opinion) the 813 is the PERFECT carb for R/C use. IF YOU ARE NOT A CONFIDENT TUNER, the 813 can be a bit tricky. It's an excellent carb if you know what you are doing and if you don't... well that's why they make the 990. Still a great carb.

In the full scale world people swear by Holley, just as others swear at them. It's all a matter of your abilities, if you can't tune a carb for poop you are going to hate a Holley, just as you are going to hate an 813. That's why the Edelbrock 600cfm is so popular, but you'll never see them on a Top Fuel dragster. Think John Force has a pair of Carters/Edelbrocks on his Top Fuel Funny Car? I think not. Edelbrock revamps old Carters to be used as street carbs for people that don't know how to tune a carb properly. Zenoah does the same thing, but Zen calls them the 668.

The same thing applies to the 813. It has an accelerator pump, something that no other small engine carb has. This little device completely eliminates the low rpm/off idle bog. It can cause tuning issues if you don't know what you are doing or if you run a 1/5th scale like you run a nitro and are constantly snapping the throttle. All of the throttle snapping shoots huge amounts of fuel into the cyl and causes the plug to foul. It's not the fault of the carb, it's the fault of the tuner/operator.

The throttle shaft wear is such a simple fix that it really shouldn't even be mentioned, but yet I still see this constantly, "The 813 has a shaft problem."

Well I guess it does, it needs a small drop of silicone/shoe goo to remedy the problem. 3 cents worth of silicone to have a perfect running carb is a small price to pay. The unfortunate thing is most of the people that have a problem with this carb is because they don't know how to tune a carb properly to begin with or are just regurgitating bullshit that they read on the internet.

There is nothing wrong with the 813.
 
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