Stock carb mod

[matesrates]

This carb is off a rotary valve engine so there is no place to install a filter, I have to stay off the dirt. I could find a way to install one but so far I have not gotten to it. Also there is a difference to the two stroke carbs, the others will work but the purpose built carb has a shield in the venture at the main jet. Have fun, Dave

PS: I wonder if this one would be a good one? http://www.zoombicycles.com/compone.../product/c689ed19b59bdf87fbb1ab779ee98267.jpg

Hey there dave
I was just reading up on some of your posts
You seem to know a bit bout these engines
So just a question
I installed a new 70cc engine today and it seems like its got no bottom end torqe
I have fitted a few of these engines but this one run no power down low
Like i go up a hill engine seem to stall when i twist at full throttle
Only way to get up a hill is to half choke it even then barely moves
Top end is fine
Please can you or anyone eles please share some light on this????????????????

 

[Masterm222]

Dontwannawalk CARB 101 Just read about your rich running. Have you done anything with the main jet? I hope you have not enlarged it any from stock. If it is stock size then lets make sure your float is set right and your needle is seating. With the carb off and the bowl off hold the carb upside down. The float should be about level with the main jet. Withe the carb upside down and a hose attatched to the gas inlet you should not be able to blow through the hose. Now that you have your float set put your carb back on. The needle that is in the top of the carb has a c-clip on it. The placement of the clip effects mixture at idle and part throttle. The longer the needle (c-clip at top) the leaner. At wide open throttle the size of the main jet is of most importance. Warm up your engine and then do a wide open (full throttle) run for minthree blocks. 1/8 to 1/2 mile. Kill the motor while at full throttle and pedal home. After the engine cools off check the plug. If it is dark brown or black then you have to make your main jet smaller. This can be done by removing the jet from the carb and soldering and drilling. Hope this helped. Let me know.

 

[Dontwannawalk]

Dontwannawalk CARB 101 Just read about your rich running. Have you done anything with the main jet? I hope you have not enlarged it any from stock. If it is stock size then lets make sure your float is set right and your needle is seating. With the carb off and the bowl off hold the carb upside down. The float should be about level with the main jet. Withe the carb upside down and a hose attatched to the gas inlet you should not be able to blow through the hose. Now that you have your float set put your carb back on. The needle that is in the top of the carb has a c-clip on it. The placement of the clip effects mixture at idle and part throttle. The longer the needle (c-clip at top) the leaner. At wide open throttle the size of the main jet is of most importance. Warm up your engine and then do a wide open (full throttle) run for minthree blocks. 1/8 to 1/2 mile. Kill the motor while at full throttle and pedal home. After the engine cools off check the plug. If it is dark brown or black then you have to make your main jet smaller. This can be done by removing the jet from the carb and soldering and drilling. Hope this helped. Let me know.

With the extra little hole (.04") in the top of the bowl to the intake chamber, would this still be true. I haven't done anything to the jet & won't be able to mess with it for a couple days. Our weather here in Iowa has turned to cold, windy & rainy. Gusts up to 50 mph. I may take the carb off & play with it some more.

Thanks for the input. I'll check the valve out...

Norm

 

[Masterm222]

I have never had a problem with idle quality so I have never bothered drilling the hole from the bowl to the intake chamber. I would think to high of a float level would cause major rich problems with that hole. Otherwise, yes, the needle comes into play at idle and part throttle. It is all main jet (and your small hole) at WOT

 

[Egor]

This is not as easy to explain. I have built I think 15 of these things, and I don't think one of them has been the same out of the box. I tried to use a few without messing with them but never was able to be satisfied with the performance. I ordered two at a time and one ran and the other had a blown case gasket. I guess if I were to take a stab at your dilemma I would blame it on the case gasket. To find out if that is the case, with the engine idling spray starter fluid under the carb (that is the most suspicious) and then around the bottom, if it is bad the engine will run better and speed up. It could be the crank seals, take the covers off and see if there is any black oil around the ends of the crank. Oil getting out means that air is getting in. I also port every engine I have, but you need to know what you are doing to keep from damaging the engine. I have put a few posts out there on porting. I hope this helps. Have fun, Dave

Hey there dave
I was just reading up on some of your posts
You seem to know a bit bout these engines
So just a question
I installed a new 70cc engine today and it seems like its got no bottom end torqe
I have fitted a few of these engines but this one run no power down low
Like i go up a hill engine seem to stall when i twist at full throttle
Only way to get up a hill is to half choke it even then barely moves
Top end is fine
Please can you or anyone eles please share some light on this????????????????

 

[Masterm222]

I agree. got to have a leak. Its to lean so you have to choke it to richen it back up but then you cant get enough air to rev. Starting fluid or card cleaner should find it.

 

[Whiplash]

I have a problem it seems as well. I have the 80cc motor from raw with a 44 tooth sprocket (I know its only 66cc) and it will not do more than about 26MPH (even on a downhill!) on a MTB and with streetish tires. It seems like it never really takes off, just kind of plugs away more like a 4 stroke till it just won't pull anymore and its gonna vibrate itself apart. I noticed I am getting a dark tan on the plug closer to chocolate and there is a wet ring arount the outer ring where the threads end on the plug. I have tried different plug gaps as well as leaning the needle out. I am wondering if I am being plagued with the leaky needle? If I try to run the choke, even with the motor cold, it sputters for a second and then dies and then I can turn it off and it will run. Any clues to these little guy carbs? I am also interested in removing the casting for the choke as it is a BIG restriction to airflow, I would like to remove it and the choke altogether and port the entry for power once I get the thing tuned right. I have a lot of engine experience just not with these little guys! I am planning on trying to lower the float level tomorrow, but just fishing for input here....

Thanks!
-Bryan

 

[leezy_1]

could you please post some pictures of how this is done exactly thanks alan....

 

[Whiplash]

OK I will post them tonight, I have to go to work! Thanks!

 

[leezy_1]

OK I will post them tonight, I have to go to work! Thanks![/QUOTE

thank you........

 

[jolfstn]

I tried the stock carb mod indicated at the beginning of this thread. I screwed up, and missed the throttle slide completely, the hole come out forward of the slide. Carb still works however, and does sort of idle a little before quitting, it didn't idle at all before. I eased off the throttle and the engine quit, no matter what I did with the adjust screw. I'm seriously considering upgrading to a CNS carb.