Roostertail carb

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Your better off with a modded 1107 over a rt990.
Thanks, there seems to be different oppinions about the 1107. I have read that actually some changes from 1107 to 990 on g320 and g340. But i don't know as i haven't tried.

However i have a stock 990 and a polished 771, which by some is rated slightly better than the 990.
My oppinion is that the 771 is a bit more responsive on my engine with stock popoff pressure.

Tonight i have played a little with the popoff pressure. The 990 pops at 38psi with stock spring.
I have cut a stock spring so that the popoff now is 16psi in the 771. (Guess the stock popoff in the 771 also was around 38psi.) This i will test tommorrow how it works.
 
@Speedloader what engine are you running? I started running the 990 on the stock 26cc in 2009 and it was like I had a different engine. At the current carb price, I'm not too concerned with the bearing mod, but you might want one if you run in very dusty conditions or sand, or have a very expensive motor. I personally haven't seen any actual reports of the throttle shaft leakage actually destroying an engine due to a lean condition, but it's a cheap upgrade for peace of mind if you're worried.

As for a full mod carb, I feel a bit dubious as to what RT does to their carbs to necessitate the "full mod" moniker, and I'm not seeing any flow or dyno tests on their site that justify the added cost. Butt dynos don't really count in this situation, but I'm sure there are many happy owners out there or they wouldn't sell them.

I agree with Sean on this one, I think if you get a standard or ball bearing modded 990 or 1107, you will be happy with the result and won't likely see a difference between the two. If you are already running the 990, I highly doubt you will see a difference between it and the "full mod" version unless you are counting lap times in milliseconds, and even then, there's no evidence to suggest it's the better carb for your kit.
 
The reason i consider upgrading, is that when hitting fullthrottle from standstill, it seems not to react right away. There a little delay - if you know what i mean.
A lot of reading indicated that the issue is the popoff pressure beeing too high.
Im on a 30.5 reed engine btw.
So today i will test the modded 771 and see if it helps.
 
I'm not running a super fast servo, so maybe I'm not feeling such a dramatic delay. But there will always be a "delay" in throttle response compared to an electric. Volts move through a system faster than go juice. That being said, you're delay may also be a tuning issue. Without a video showing the actual response times, it's impossible for me to make any kind of judgement.

OBR uses unmodified WT-990s for all of their 30.5 Full Mod Reed Case Engines and continue to use them on the 32-34cc version as well. I would imagine that if they saw the same problem, they would not use them, or offer some form of mod for these carbs. These guys have been tuning and modding these motors for almost 2 decades, so they know the score.

If you think this lag is a bit too much, you might want to reach out to them to see if maybe they can offer some tuning advice if you are running a 990 or 1107.

Hopefully you find something that will hit all the notes for you!
 
I'm not running a super fast servo, so maybe I'm not feeling such a dramatic delay. But there will always be a "delay" in throttle response compared to an electric. Volts move through a system faster than go juice. That being said, you're delay may also be a tuning issue. Without a video showing the actual response times, it's impossible for me to make any kind of judgement.

OBR uses unmodified WT-990s for all of their 30.5 Full Mod Reed Case Engines and continue to use them on the 32-34cc version as well. I would imagine that if they saw the same problem, they would not use them, or offer some form of mod for these carbs. These guys have been tuning and modding these motors for almost 2 decades, so they know the score.

If you think this lag is a bit too much, you might want to reach out to them to see if maybe they can offer some tuning advice if you are running a 990 or 1107.

Hopefully you find something that will hit all the notes for you!
Well its not a tuning issue as i have tried a lot of needle settings. Its maybe just me beeing sensitive about it, its not that bad, its just not reacting that fast. But surely faster with the 771 than the 990.
I will try the popoff mod in the 771 and keep you updated. I have only read positive about this mod in combination with reed engines.
 
@Speedloader If you are running a WT-990 or WT-1107 and want to do a pop off mod, the WT-257 spring will do the trick if you aren't willing to clip some coils. This should drop your pop off to lower than 19 PSI. The carb is discontinued, but I did some digging and found one for ya: https://www.jackssmallengines.com/jacks-parts-lookup/part/walbro/983047 and you can buy a 5 pack here: https://www.mowers4u.com/983047-pack-walbro-metering-springs-p-2775.html.

This is the spring that was recommended for the 990/1107 for 30.2 Reed Case motors according to my research.
 
@Speedloader If you are running a WT-990 or WT-1107 and want to do a pop off mod, the WT-257 spring will do the trick if you aren't willing to clip some coils. This should drop your pop off to lower than 19 PSI. The carb is discontinued, but I did some digging and found one for ya: https://www.jackssmallengines.com/jacks-parts-lookup/part/walbro/983047 and you can buy a 5 pack here: https://www.mowers4u.com/983047-pack-walbro-metering-springs-p-2775.html.

This is the spring that was recommended for the 990/1107 for 30.2 Reed Case motors according to my research.
Alteady cut some coils and pressure tested it to 16psi
 
Thanks for the information,appreciated.
So my obr 29.5 FM LB, came today?
So I guess I'll use 990 since I have it,for the moment anyway.
So I took off the carb on 23(25.4) ESP head and it's running a wt603. Any info on this carb?. I had put the 990 on but haven't tested. The 23 ran rich w/603 but needed tune. So I'll still have to get another carb unless someone says wt603 is good.
 
Thanks for the information,appreciated.
So my obr 29.5 FM LB, came today?
So I guess I'll use 990 since I have it,for the moment anyway.
So I took off the carb on 23(25.4) ESP head and it's running a wt603. Any info on this carb?. I had put the 990 on but haven't tested. The 23 ran rich w/603 but needed tune. So I'll still have to get another carb unless someone says wt603 is good.
It didn't come today if you don't have pictures ???? wanna see plz
 
Ok so the 603 and 668 are stock carbs on the smaller cc engines. The 990 and 813 are the same with one exception the 813 has an accelerator pump. The 1107 has a slightly larger bore and venturi then the 990 or 813. It also has a choke and slightly different metering (if memory serves) so in the grand scheem of things your 603 will be fine, but may be laggy in the bottom end when tuned right.
Oh I forgot to mention the 603 and 668 for all intensive purposes are the same. I think the 668 has a slightly larger main jet passage or it may have been the fuel Inlet. But for rc they are in the same performance category to me.
 
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