walbro carb

Firestorm102389 · Feb 1, 2014

There is a stage 3 walbro carb that uses a crankcase vent to pump fuel in, it's off jnmotorsbikes.com. I was wondering if this would even be worth the money? I'd be putting it on a mountain bike with a 36 t sprocket and voodoo expansion exhaust. The kit originally comes with a speed carb, and the reviews on that walbro one seem to hold up well and great performance. I just want to hear anyone else's experience with it. I don't want to spend the money if the carb isn't any better. May use the bike for some off road use, lightly.

Thanks in advance!

maniac57 · Feb 1, 2014

I have had great luck with the walbro carbs on rc engines for decades although I have never used one on a HT.
They are very high quality and very tuneable as well. Also easy to find parts for.
I would not hesitate to try one if you are interested.
Be aware you will need to install a vacuum line to the engine for the fuel pump diaphragm to operate correctly on most versions.

Firestorm102389 · Feb 1, 2014

That vacuum line I already knew, there is an m4 hex head I could drill a 2 mm hole in for it, or I'm thinking a blessed screw for an automotive brake caliper might do it as well. That's the response I was looking for, thanks. I'm going to try it and tune it in. I've been building these for a year now, about 10 projects behind me, any tips on tuning the carb or is checking the spark plug the best way?

maniac57 · Feb 1, 2014

Just read the plug with normal plug chops. Keep in mind some are more sensitive to mixture screw settings than others and keep the adjustments small when you get close. Also be sure the vacuum line you use does not collapse under engine vacuum. I've seen this cause mysterious tuning inconsistency and is very hard to diagnose if you don't know to look for it.
I also highly recommend you use a good stout return spring as these carbs won't close by themselves if the cable breaks quite often. Some have very weak return springs from the factory.
As long as the carb you use is from a two-stroke engine close to the same cc's you should be in the ballpark on jetting to start out.

silverbear · Feb 1, 2014

Please share your results for everyone's benefit. By the way, welcome to the forum!
SB

Firestorm102389 · Feb 1, 2014

Thanks for all the info, yeah, I'll deffinitely share the info. As soon as I get my taxes back, I'm working with a friend of mine to build and tune it. You all probably know him, Donovan. I met him a while back after I had built a few of mine already and we decided to team up and I have the funds to try it real soon.

Firestorm102389 · Feb 1, 2014

Ps, the carb from jnmotorsbikes is for the 66/80cc motor so I think it will be great. The reed valve should help a lot too, so I'll let everyone know how it all goes and how we went about installing it.

silverbear · Feb 1, 2014

Firestorm102389 said:
Ps, the carb from jnmotorsbikes is for the 66/80cc motor so I think it will be great. The reed valve should help a lot too, so I'll let everyone know how it all goes and how we went about installing it.

Good...
SB

Donavan321 · Feb 2, 2014

Firestorm102389 said:
Ps, the carb from jnmotorsbikes is for the 66/80cc motor so I think it will be great. The reed valve should help a lot too, so I'll let everyone know how it all goes and how we went about installing it.

Thanks firestorm, looking forward to working with you as well. Pictures are pretty helpful during builds, so we should take lots of them, also you should post in the "introduce yourself" and meet some other members! Was glad meeting you yesterday, the women talked and we did our thing lol. I've seen people use all kind of different carbs on the HT engines(Ht= happy time, also called chinagirls) the SHA carbs are pretty good as well.

16v4nrbrgr · Feb 2, 2014

My Preddy auger powered BMX has a Walbro style pumper carb on it, and I am impressed with its easy starting, and performance. You can tune it easily to suit the day's weather conditions, and it can be tuned for certain parts of your ride, like richening the top end mixture when you are going to hit a long hill and don't want the motor to run lean and overheat. It atomizes the fuel really well, and it's worth playing around with using different heat ranges of spark plugs. I was able to pick up quite a bit of power by tuning the top end richer and using a hotter plug.

Firestorm102389 · Feb 2, 2014

What plug are you using? I was thinking an rs8 or rs7

16v4nrbrgr · Feb 2, 2014

It totally depends on what engine you're using, the particular cylinder, piston, head, gasket thickness, squish band clearance, pipe, and carb, along with weather conditions you'll ride. Generally a 2 stroke likes between a 5-8 heat range plug.

Firestorm102389 · Feb 2, 2014

I'll probably get a 7. I'll have a voodoo expansion chamber exhaust, on an 80cc 2stroke.

seb1008 · Feb 3, 2014

I will be following this. I would like to use the walbro carb. I am just now buying parts to rebuild the new 66cc that has a jackshaft on it. That i bought last week. I am going to northern California in a few months to use it on forest service roads looking for gold. I was thinking about a mikuni 18vm with an extended manifold but it seems complicated with all the jets and fine tuning. It seems like the walbro is simpler. Could you set the walbro up with out the reed valve? I have read everything I can find on the walbro, not a lot of info except what Fabian has posted. I will hold off on buying a carb and wait and see how this build goes.

Firestorm102389 · Feb 3, 2014

The main thing is if you don't have the reed valve you need some sort of spacer so you don't ruin the diaphragm and boil the gas before it gets in the engine. Reed valve is recommended because it keeps the entire air fuel mixture in the crank case when the piston goes back down instead of spitting that little bit back out, so you get more power.

seb1008 · Feb 3, 2014

Ok, thanks for that. I would get the reed valve but do you know where you can buy the spacer? I have read about it being necessary to seal properly even with the reed valve.
Reading what 16v4 about how easy they are to adjust it seems like the walbro would be just what I need in the mountains.

16v4nrbrgr · Feb 3, 2014

The main thing is if you don't have the reed valve you need some sort of spacer so you don't ruin the diaphragm and boil the gas before it gets in the engine.

You just need the proper intake manifold for the carburetor with the crankcase pulse channel to make it work. These carbs come on every piston ported pocket bike engine sold, which are also used as utility engines on chinese lawn and power equipment.

Firestorm102389 · Feb 4, 2014

Can't get the thermal spacer in the states unless you make it. Reason being, I looked. Get the reed valve and it should be far enough from the engines heat to be ok.

seb1008 · Feb 4, 2014

Thanks, i thought that might be an issue. I am going to check with arrow about using their reed valve with the walbro.
What is the difference between the three stages of walbro on JNMs sight? I do not need high end speed, just torque for pulling a trailer and going up mountains.
Sorry for hijacking your thread, I appreciate your helping me out.

Firestorm102389 · Feb 4, 2014

Np. Stage 1 and 2 are the exact same, so don't buy stage 2. Stage 3 is bigger and going to allow more power. You might not need the high speed but you'll get more power. I recommend the jackshaft kit for the hills and stuff over a standard sprocket, allows for more of a power band. I can't remember if you said you were getting it or not. I built one of those, hard to sell, and only worth it for off road use. Standard kits are great for driving on roads.

walbro carb

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