Walbro WT 990

G-Man · Apr 28, 2017

I have a walbro 990 carb on my zenoah engine. It has been great for the past 6 months. On day I ran a half a tank of gas and shut it off to run another rc. Came back to restart the engine as I always do. I noticed there was no fuel in the primer bulb, so I pushed it 3-4 times and it wouldn't fill again. So I'm guessing the carb needs rebuilt. My question is, Does the entire carb need torn down and rebuilt or can I replace the gaskets/diaphragms only to resolve this issue? I have never rebuilt an rc carb so any advice would be appreciated. Oh and I have the fuel tank vented. I also tried to crack the fuel cap thinking maybe my vent valve is clogged. The primer bulb still wouldn't fill. Thanks

designed2survive · Apr 28, 2017

@G-Man

It may be as simple as needing a new prime bulb which is easy to replace.

But first I would remove it from the engine (keeping the fuel line connected) and prime it to see if fuel is going through.

G-Man · Apr 28, 2017

designed2survive said:
@G-Man

It may be as simple as needing a new prime bulb which is easy to replace.

But first I would remove it from the engine (keeping the fuel line connected) and prime it to see if fuel is going through.

G-Man · Apr 28, 2017

See if fuel is going through where? Thanks

Phill2 · Apr 29, 2017

G-Man said:
I have a walbro 990 carb on my zenoah engine. It has been great for the past 6 months. On day I ran a half a tank of gas and shut it off to run another rc. Came back to restart the engine as I always do. I noticed there was no fuel in the primer bulb, so I pushed it 3-4 times and it wouldn't fill again. So I'm guessing the carb needs rebuilt. My question is, Does the entire carb need torn down and rebuilt or can I replace the gaskets/diaphragms only to resolve this issue? I have never rebuilt an rc carb so any advice would be appreciated. Oh and I have the fuel tank vented. I also tried to crack the fuel cap thinking maybe my vent valve is clogged. The primer bulb still wouldn't fill. Thanks

Parts are available at DDM but having owned a 990 myself I'd chuck it and put a 668 on

G-Man · Apr 29, 2017

Phill said:
Parts are available at DDM but having owned a 990 myself I'd chuck it and put a 668 on

Hahaha. Chuck it. I have a rebuild kit from ddm thanks. I was just wondering if it should be completely torn down or just replace the 2 diaphragms under the primer bulb. I may try a 668 though

G-Man · Apr 29, 2017

designed2survive said:
@G-Man

It may be as simple as needing a new prime bulb which is easy to replace.

But first I would remove it from the engine (keeping the fuel line connected) and prime it to see if fuel is going through.

I have an alloy insulator I've been wanting to put on. Will give me reason. Should I tear the whole carb down and replace every part or ya think just the seals?

Phill2 · Apr 29, 2017

G-Man said:
Hahaha. Chuck it. I have a rebuild kit from ddm thanks. I was just wondering if it should be completely torn down or just replace the 2 diaphragms under the primer bulb. I may try a 668 though

If you check the specs the 668 is the same carby but has a choke.
Same bore , venturi etc
Makes life much easier

G-Man · Apr 29, 2017

Phill said:
If you check the specs the 668 is the same carby but has a choke.
Same bore , venturi etc
Makes life much easier

I really havn't had any starting problems till now. I don't use a choke anyways. I'm going to take the time to tear it down completely and rebuild it. Walbro has an awesome 20 minute video doing a rebuild in detail. Once I am done with my dunerunner project. I was looking for an easy way out, which in the past has bit me so this dude is doing it right to save pain later lol

fordgtr06 · Apr 29, 2017

DDM is running a sale on the 990 right now!!! I just ordered one. Did you notice an increase in performance with yours over stock? And are they easy to tune?

G-Man · Apr 30, 2017

fordgtr06 said:
DDM is running a sale on the 990 right now!!! I just ordered one. Did you notice an increase in performance with yours over stock? And are they easy to tune?

Hey whats up. Yes big increase in performance. I set it at the factory needle settings and pulled it 4 or 5 times and it was idling. I leaned each needle a 1/16 turn give or take after it warmed up. Thanks for the info on the ddm deal BTW. I got one today too as back up. I will put it on my MT and rebuild mine in the meantime

fordgtr06 · Apr 30, 2017

G-Man said:
Hey whats up. Yes big increase in performance. I set it at the factory needle settings and pulled it 4 or 5 times and it was idling. I leaned each needle a 1/16 turn give or take after it warmed up. Thanks for the info on the ddm deal BTW. I got one today too as back up. I will put it on my MT and rebuild mine in the meantime

Great. I'm excited to get it on. What are factory needle settings? I'm sure I could find them in the manual but if you know off the top of your head that would be great. And no problem, I have been checking it everyday hoping they would go on sale. I was about to buy one anyway and saw they were on sale.

G-Man · Apr 30, 2017

fordgtr06 said:
Great. I'm excited to get it on. What are factory needle settings? I'm sure I could find them in the manual but if you know off the top of your head that would be great. And no problem, I have been checking it everyday hoping they would go on sale. I was about to buy one anyway and saw they were on sale.

fordgtr06 · Apr 30, 2017

Thanks G-Man. I out a cpi pipe on my mt. Sounds better. Not as raspy as the redcat tuned pipe.

G-Man · Apr 30, 2017

I find 1/8 turns difficult to do so I made it into

fordgtr06 said:
Great. I'm excited to get it on. What are factory needle settings? I'm sure I could find them in the manual but if you know off the top of your head that would be great. And no problem, I have been checking it everyday hoping they would go on sale. I was about to buy one anyway and saw they were on sale.

Do you use ddm in the coupon code box for 5% off? If not next time. Usually it will take care of shipping or at least helps..

fordgtr06 · Apr 30, 2017

G-Man said:
I find 1/8 turns difficult to do so I made it into

Do you use ddm in the coupon code box for 5% off? If not next time. Usually it will take care of shipping or at least helps..

No I haven't been but I will start. Thanks.

G-Man · Apr 30, 2017

fordgtr06 said:
Thanks G-Man. I out a cpi pipe on my mt. Sounds better. Not as raspy as the redcat tuned pipe.

CPI pipe huh. That is cool!! They aren't made anymore right?

fordgtr06 · Apr 30, 2017

G-Man said:
CPI pipe huh. That is cool!! They aren't made anymore right?

No there not. I found one on eBay that needed brackets made for 50 bucks. So I made some brackets and polished it up.

G-Man · Apr 30, 2017

fordgtr06 said:
No there not. I found one on eBay that needed brackets made for 50 bucks. So I made some brackets and polished it up.

Looks good man wow!! Almost nobody has one. I think they were a popular secondary choice for the V1 and V2 MT over the jetpro

fordgtr06 · Apr 30, 2017

G-Man said:
Looks good man wow!! Almost nobody has one. I think they were a popular secondary choice for the V1 and V2 MT over the jetpro

Yeah it sounds good. Do you have a jet pro on yours? I'd like to get one but I couldn't pass this cpi up for 50 bucks.

Walbro WT 990

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