tskdave

Have new mti cat, w/toxic marine venom motor. I think it has a zero band alm. pipe. Looking for help tuning....spent 3-4 hrs 1 gallon of gas. Running 275 prop, 7016 2 blade on order. Fastest I got was 30 on gps?????? Looking for stock needle settings. have been in rc for 15 years....not new to motors.This is my first boat. I have leaned/richened the motor till it won't run. Nothing seems to help. Pipe lengh???? Can't seem to get on the pipe. I have talked to Alan many times......This guy knows his stuff!!!! I didn't want to bother him on labor day!!!!! Any ideas???? The pipe is now all the way to the back of the boat, moving it closer seemed to make it worse.Please help.....Thanks, Dave

Tell 1uk

Hi what carb are you running? what pipe are you using? where is the strut placement in relation to the hulls?without this info its going to be hard to give you a answer.

martno1fan

hi does this help any ?

tskdave

Carb is a 603A. We tried moving the strut all the way up and down.We started at 1/2"above bottom of boat(on a table to center of shaft).Changed a little but not much. I don't know the brand of the pipe. I purchased it from Expresscraft w/the motor. Thanks, Dave.

tskdave

sorry, 3/8" to 1/2" ABOVE the bottom....hope this helps. Dave

Tell 1uk

The strut should be set with the prop hub center level with the bottom of the hulls you should not have to move to much from this point, if you were too high as it seems you will lose power and bounce the boat... the carb I am not fimilar with, is it a walbro? the pipe settings can be anything from 12-15 ins see marts diagram this length should get you started (14 ins say) then fine tune from there.The carb used on most tuned motors is the 257 walbro perhaps its worth changing ! or find the base settings for your carb? check for manifold and exhust for leaks as this can stop the pipe from working properly.

glennb2006

Hi Dave,

ref the pipe. You really need to start at a long tuned length, say about 350mm, then work forward (shorter) from there. You said that you had the pipe all the way back now - you have trimmed (chopped) the header pipe haven't you, ie you do not have about 4 inches of header sitting inside your expansion chamber do you?

I know it's a daft question and no insult intended, but I have seen it before.

Other than that, free drive, correct mixture and right size prop on a half decent trimmed boat should get you to a point where you can set out, IE boat planing then work on trim to fine tune etc.


Glenn

tskdave

Carb is a Walbaro, it came with the modified motor. I should clarify about the pipe. The pipe is back about as far as it will go. Tere is maybe 1"of header left. (the pipe is as long as I can make it).I still can't seem to get the front of the boat out of the water. At full speed, it is still seems to "plow" threw the water. Raising and lowering the strut does not make that much diference.(I thought this is due to the motor not being tuned right. As a dumb question, should I move the pipe as far forward and re-tune?? Maybe going from one extreme to another???? Thanks for all the help, Dave.

xxxboatworks

I provide Expresscraft with thier exhaust systems. I'm also familiar with the toxic engine and mti hull. The pipe should be tuned between 11 7/8 and 12 1/4. The center of the prop shaft needs to be about 3/8" above the bottom of the sponsons. Drive should have a degree or two of negative angle. Hope this helps.

Paul M

What's your C of G? I would think you would want it less than 32%. If it's too far forward, I'm sure the boat would plow.

Also what is the weight of the boat?

I had an MTI. I ran it with a Mathe 35 and was able to get 51mph. I tried a SIKK 27 which is about the same HP as yours and couldn't get more than 35 with a X472. Mine ready to go was about 22# (with the SIKK - 26 with the Mathe) and the cg was about 30%. It's a huge boat. Maybe it's a little too much hull for that engine?

I can send you a film of mine running with the SIKK if you want.

tskdave

I have not checked the cog. What %do I want for this boat?? If it is way off how would I fix it, w/o moving the motor??? Thanks for all the replies.

Paul M

Like I said, I think it should be about 30% ,but I have built one. Check with Tom or Raj (XXX Boat works) who have built many.

If it's way off, you'll have to move the engine to fix the CG. I suppose you could add weight in the bow, but note the tuning suggestions Raj offered before you do anything drastic.

Al at Toxic is a great guy and should be able to help you rule out any engine woes.

Alot of times when you get frustrated, you think you've tried everything when you haven't. If your anything like me your probably making it more complicated than it is.

grant118

My Feedback: (26)

Paul,

Send me a copy of the video also. I am interested in the MTI boat also. I think I will run dual zenoah's, to your point, this is a big boat. I am building a systems cat right now and it is a heavy boat.

Chris

Paul M

Grant, YGM

fred745

i gps my mti 44 mph with stock zen an a tater from vodoo props.

Paul M

Tater?? So where's Snuffy and 'weezy??

toyingaround

I just built a MTI Cat with a QD25 HT & QD pipe in her.
The engine should be mounted so that 12.5" from center of spark plug hole to rear inside of transom.
The strut as they are telling you should be 3/8 to 1/2" above the sponson.
I ran a Propshop 7015-2 & 3 blade on it & pulled 50 MPH off the workbench with no ajustments.
I figure with some fine tunning it should run in the high 50's
The strut does need about 1 to 2 degrees of neg in it, as the boat is really squarely once up out of the water and running.
This boat likes rough water to get the air packed under it.
I ran mine on a 4" chop & she was up & gone in about 20 feet
They will run on smooth water, but you have to find that sweet spot on your strut adjustment & the right prop.
As far as your header & pipe, 12.5" from exhaust port to the center band of the pipe, measured on center line of the header and pipe.
Make sure you only have about 2" of header stuck inside the pipe.
Carb settings on most engines, I start at 1.5 turns on both high & low needles.
Start with the low side and lean it out slowly till it is really zippy, (your RPM's will come up so you'll have to use your trim lever on radio to lower rpm's,) don't lean it to much though you'll know when to stop by the engine bogging when you hit the throttle.
Then go to the high side and do the same, you will need to do this on the water, if it boggs when you punch it, lean it out a 1/8th turn and do it again, keep doing till it is screaming, then richen it up 1/8th turn.
Props, I would start with the 275 or 7015 once you get it up and running good, then you can try others.
Hope that helps
Cheers
Carl

tskdave

Thank you everybody for all the input. I have allready learned alot from this site. I think the only thing we have left to try is changing the carb. Right now it has a 603. I talked w/Alan at toxic and he said we will try the 257. I will keep everybody posted. Thanks again, Dave.

xxxboatworks

I spoke with Alan in great length about your boat yesterday. The 257 is on the way and hoefully cure the problem.

tskdave

tried the 257....same thing. Almost seems way to rich. Amsoil first mixed @6OZ . then tried 4oz. still no change. Motor still will not get warm.....new fuel lines/gas tank, checked for air leaks, new plug. Pipe set @12" running out of options.....any ideas?????? Running 275 prop. Started new carb setting 2 low 1 high. Ideas????

simonmiller

Does it sound like the engine is not getting to the top end when you open up the throttle?

I have just been tuning a BZ4 Zenoah from Bonzi on my Blackjack, after messing around with all things mentioned so far I changed my prop and suddendly I had a top end.

Just my two cents but worth a try!

Simon

Tell 1uk

Just an Idea, I couldn't seem to tune my mod Zen tried all settings in the end with the help of a friend (he held it) I tuned it in the water for top end, it took about 30 secs and then run perfect with just minor changes on the low needle.

tskdave

I tried leaning the high and leaving the low end alone. The low had to be set about 11/2 for a good idle and response. The high was about 7/8,still wouldn't respond. I have also tried riching the high w/ low set 1 1/2, same thing. The only thing I have not tried:
Setting the low at 2 and leaving it.....and just tuning the high end. Like I said it is so rich it will hardly run at 2 turns out?? I thought adjust the low end first then the high. Should I try leaving the low at 2 and just adjust the high???? Scared its going to die in the middle of the lake!!!!! Thanks, Dave

simonmiller

Q: What are the high/low settings for my carb?

A: Stock Walbro WT-644 carb
High = 1 1/2 turns
Low = 1 1/2 turns

Stock Walbro WT-603 carb
High = 1 1/2 turns
Low = 1 5/8 turns

Walbro WT-488 big bore carb
High = 1 1/8 turns
Low = 1 1/2 turns

Walbro WT-257 big bore carb
High = 1 1/8 turns
Low = 2 turns

Walbro WT-813 big bore carb
High = 1 1/2 turns
Low = 1 1/2 turns

simonmiller

Boat runs fast for a short time then slows down when at full throttle.
Carburetor high speed needle to lean. Open needle counterclockwise in 1/8 increments between water testing.
Engine stalls or runs very hot.
Water pump or cooling lines clogged. Check water pick-ups, pump and hoses for internal debris.
Engine sounds raspy or misses.
-Carburetor high speed needle to rich. Close needle clockwise in 1/8 increments between water testing.
- If your engine has a choke, make sure it is fully open
Engine surges at full speed.
- Low fuel.
- Fuel cap breather hole clogged (clean/replace)
- Fuel pick-up lines reversed.
Clutch will not disengage.
- Engine idles too high. See carburetor adjustments.
- Clutch bolts rusted or dirty. Clean or replace.
Engine revs up, clutch will not engage.
Clutch shoes and or clutch bell worn. Must be replaced.
EXHAUST SYSTEM:
Large amount of black oil is evident inside the hull.
- Tighten exhaust manifold or canister.
- Replace exhaust gasket.
- Replace exhaust coupler.
Exhaust header loosens up after running.
Check exhaust manifold screws and tighten if necessary after each days use. If problem persists, change exhaust gasket. Do not use thread lock on exhaust manifold bolts.