CMB90 carby mods

[westoz]

Gday all currently running a cmb90 with stock carby in my seaducer when running down saw 3/4 throttle is fine but wont clean out at full, feel carby isnt supplying enough fuel what mods can i do drill out fuel inlet perhaps .

using 40%

macs nitro pipe 12.5"

X665 prop

thanks dave.

 

[BradV]

Dave why not go up to 50% nitro and try that? Seems from recent info posted here the CMB90 prefers 50%.

Other thing after our chat last week at the lake I went home and had a serious look at the tank I'm using with my CMB.

Ended up re-building it with oversize brass tubing - the way the tanks come is pathetic - they have about 3/32" brass tubing. I changed it to 3/16 ID - was fiddly but looks a real treat.

 

[TimD]

3/16"ID :blink:

The stock carb should be fine on 40%. check your pressure nipple in the pipe and the pressure line for holes etc.

 

[westoz]

Gday brad I havent run boat since last meet reading some of the posts on fuel mixes I think i will try 50% I am using larger brass on tanks just that I have heard that stock carbs on cmb are better modded for better throttle control oh well i will keep experimenting.

How's your hull coming along.

Dave.

 

[westoz]

Tim I change fuel lines on regular basis pipe nipple seems fine.

 

[EatMyShortsRacing]

Try using the Seaducer M(?)90 or 91 prop. Unloads better than an X665 and with the amount of material you need to remove to balance an X665 you are likely to fold a blade over when it does come on hard...

Other thing may be to tune it on an X465 and try richening the bottom end up and leaning the top end.... sounds like it is possible you are getting too much fuel at the top end???? Easy way to tune is to richen up the top end, open the carb full (should be 'four stroking' so not getting anywhere near full rpm) and lean out slowly till it revs out. shut it down as soon as it looks like it will rev out and then wind the bottom end out a fair way... take it out and only worry about full throttle tuning till you get the top end right..... then look at what happens when you back off.... if it wants to keep going then richen the bottom end....

 

[westoz]

Cheers all have taken all tips on board.

 

[DaveMarles]

For those using the R/C needle version of the later CMB 90 carbs. We had some where the spraybar was not drilled all the way through and this left only a small hole at the end.

 

[BradV]

3/16"ID  :blink:

Yep can't have too much of a good thing bud

 

[TimD]

3/16" is what size the flex cable is in my 21 rigger. I don't run lines that big on my thirsty 90 engine...... 5/32" perhaps?

 

[westoz]

yeah 5/32 is what im using

bugger if i get 65mph out of my 44" duce i recon im doin alright.

 

[Roxyflash]

What needle vavle are you using third channel or fixed type?What size is your spray bar ?Using a low needle?What pipe length?Taking the plug or not?

 

[EatMyShortsRacing]

yeah 5/32 is what im using bugger if i get 65mph out of my 44" duce i recon im doin alright.

Well I got 60mph with a stock X465 on the back of mine so 65 is pretty achievable Now running the M91 and I believe it is quicker again but dont have data to back that up.

EMS Racing mph coz clocked in the US

 

[TimD]

bugger if i get 65mph out of my 44" duce i recon im doin alright.

Absolutely! B) That is fast enough to win a lot of races.

 

[EatMyShortsRacing]

bugger if i get 65mph out of my 44" duce i recon im doin alright.

Absolutely! B) That is fast enough to win a lot of races.

hey Tim, does mine look fast enough??? All I need to do now is be able to drive it!!!

 

[Ian Inverarity]

Actually I won plenty of races with a 50mph boat! B) Required good starts and tight driving tho...

Hopefully the new engine/pipe/hull combo will be good for 70!

Nitrocrazed racing: Need new P&L.

 

[TimD]

hey Tim, does mine look fast enough??? All I need to do now is be able to drive it!!!

Craig,

When your X mono is running right - it is probably the fastest 'ducer I've ever seen. I was very impressed by it @ Canberra.

Ians Kingy always seems to get 2nd place I think that will change this year.

Mine is still not finished :blink: :blink: hopefully the thing will get wet before the nationals :lol: :lol:

Tim.

 

[EatMyShortsRacing]

Tim,

Gotta fix that damned mixture servo one day!!!

EMS Racing too many broken bits

 

[Mike Broad]

I think this thread has lost the plot. The original question was about fuel starvation at full throttle. Dave Marles made a valid point. I know of at least one boater that has trashed an engine, rebuilt it and had further problems only to find that it was because the carburettor spray bar was drilled undersize. I know he is only a beginner boater but Dave does know what he is talking about

Mike Broad

 

[EatMyShortsRacing]

I think this thread has lost the plot. The original question was about fuel starvation at full throttle. Dave Marles made a valid point. I know of at least one boater that has trashed an engine, rebuilt it and had further problems only to find that it was because the carburettor spray bar was drilled undersize. I know he is only a beginner boater but Dave does know what he is talking about

Mike Broad

Well yes and no..... A couple of people have pointed to the starving at full throttle or possibly too ruch at full throttle.... not really enough information to tell which is the problem as yet...

Dave (well respected and in my opinion one of the most reliable sources of knowledge on this board) may be right... There could be other problems instead and until we get further information or go out ther ourselves (Perth is a bit far for us Melbournians so I cant see Dave making the trip ) we are just providing possible problems. So we have posted our reccomendations and so far no further info has come back....

While we are here we may talk a lil shite to fill in time......

Just dont assume that because Dave posted a possible solution that he has solved the problem for that particular boater. Its like saying to a doctor I have a cough.... There could be 10 different reasons for that so without further investigation all we can do is provide different solutions based on our guess at what is happening from the info given,,,,

Waiting on further info from WestOZ