Something you should know about the 813 carb

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DemonRC1

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I figured I'd post this up since I just figured this out. I'm sure alot of you guys know about it, however, it's good information for the newer guys. Anyways, I've had alot of problems with my... umm... 7th 813 carb. It wasn't the typical air leak from the wobbly throttle shaft. For the last few weeks it's taken me forever to start my car. Typically, I pump the gas 10 times and 3 or 4 pulls later it starts. Now it's taken me 20-50 pumps to get this thing going. Well I figured it out and hopefully this helps somebody in the future. Here's it goes:


The 813 does not have a choke like the 668 instead it has an accelerator pump. The pump is operated when the throttle is opened. What this does is squirt fuel directly into the intake for faster throttle response. Ok, most of you guys know that but here's something you may not know. In front of the throttle butterfly there is a nozzle at the top of the intake bore. That is the nozzle for the accelerator pump. Watch it closely as you repeatedly pump the throttle and you will see gas squirt from that nozzle. So I saw my accelerator pump WORKING!?!?! That didn't make sense. How come my car won't start when gas is getting squirted directly into the intake? I figured it out. All the gas was running forward and getting soaked up into my air filter instead of being sucked backward into the engine. The reason why is because I've started to start my car with my left knee of the front bumper which leans the car forward causing all the fuel from the accelerator pump to run forward into my air filter. So I leaned the car back for $%ts and grins, primed the throttle 5 times, and it started right up.


To sum it all up. If you wanna start ur car real fast with an 813, lean it backward when priming the engine. Don't be an idiot like me and lean it forward.
 
Last edited by a moderator:
rpking said:
Does the 813 carb make a big difference in performance over the stock carb on a stock engine?
Click to expand...
Not a big difference. You get a slightly snappier throttle when coming off idle. It just takes away that little lag when punching the throttle from idle.
 
tuning 813 ?'s


i just cant seem to tune my 813 right wen it runs it is supper snappy and fast but its almost like it runs out of gas or something i have no problem starting or idle but a wide open it almost always spits and sputters would this be a air leak or tuning issue thanks for the help
 
Spit and sputter would defintely mean it's lean at WOT. I'd reset my needles, get my low end right and then retune the top end.
 
i am having the same problem with my mt,i put a new 813 carb on mine,tried a new coil,new plug,but mine still breaks up at wot.called redcat,he said the only thing that would cause that would be it was sucking air.well i have sprayed carb cleaner on every gasket and found nothing.so they told me to send the engine to them since it was still under warranty.unless someone else has any other ideas.
 
DemonRC said:
I figured I'd post this up since I just figured this out. I'm sure alot of you guys know about it, however, it's good information for the newer guys. Anyways, I've had alot of problems with my... umm... 7th 813 carb. It wasn't the typical air leak from the wobbly throttle shaft. For the last few weeks it's taken me forever to start my car. Typically, I pump the gas 10 times and 3 or 4 pulls later it starts. Now it's taken me 20-50 pumps to get this thing going. Well I figured it out and hopefully this helps somebody in the future. Here's it goes:
The 813 does not have a choke like the 668 instead it has an accelerator pump. The pump is operated when the throttle is opened. What this does is squirt fuel directly into the intake for faster throttle response. Ok, most of you guys know that but here's something you may not know. In front of the throttle butterfly there is a nozzle at the top of the intake bore. That is the nozzle for the accelerator pump. Watch it closely as you repeatedly pump the throttle and you will see gas squirt from that nozzle. So I saw my accelerator pump WORKING!?!?! That didn't make sense. How come my car won't start when gas is getting squirted directly into the intake? I figured it out. All the gas was running forward and getting soaked up into my air filter instead of being sucked backward into the engine. The reason why is because I've started to start my car with my left knee of the front bumper which leans the car forward causing all the fuel from the accelerator pump to run forward into my air filter. So I leaned the car back for $%ts and grins, primed the throttle 5 times, and it started right up.


To sum it all up. If you wanna start ur car real fast with an 813, lean it backward when priming the engine. Don't be an idiot like me and lean it forward.
Click to expand...
Very informative thread! thanks for posting it. I have just put on the 813 on my MT a week ago, so far I don't have any problem yet.
 
kcollier said:
i am having the same problem with my mt,i put a new 813 carb on mine,tried a new coil,new plug,but mine still breaks up at wot.called redcat,he said the only thing that would cause that would be it was sucking air.well i have sprayed carb cleaner on every gasket and found nothing.so they told me to send the engine to them since it was still under warranty.unless someone else has any other ideas.
Click to expand...
I've also had my high end do this on one of my first 668 carbs. Richening the high end seemed to have absolutely no effect on the WOT sputtering. I took the carb apart and there was dirt in the diaphram (under the fuel bubble) and dirt particles inside other places. I figured dirt was clogging the high end somewhere so I pulled it part and sprayed it out with carb cleaner that had a high pressure stream. It worked like it was brand new after that.
 
that will be cool if it is just running lean on the high end i just was adjusting them and got it to idle good and then it runs good and then sputters so i hope it will solve the problem i am in the middle of putting dual servos on it so i will be a little bit before i get it out again and my plug looks like a light black
 
If it's more like a grayish color and dry then that would indicate a slightly lean mixture. I bet if you richened it 1/8 of a turn you would get the plug nice and brownish which is where you want it.
 
had the mt out today and finally got my 813 tuned in great alot of my problem was coming from my tank vent that was almost plugged up once i got that cleaned i was off to the races and staying on top of the snow (14") of snow so it was running really nice thanks for the tips on the plug color and what to do it it is sputtering it was also a little lean
 
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