K&B 3.5 Won't Go Around One Time!

[TUNLBOTR]

On the 3.5 the front plate will develop a hairline crack down the side of the big bearing, its a typical tolerance issue on older KB's. ALSO check the end of the drive dog where the flex shaft joins, if it cracks the motor will run until load is applied, the shaft will load against the crack, spreading the inside clearance and will bind, causing shutdown... I had a handful of these failures alone in '06, so did AFI Racing, all at National events, even at Charleston. Just throwing angles at ya.

Randy

 

[jaxracer]

I did re-position the brass fuel pick-up tube in the tank. It is now located in the right hand back corner of the tank (closest to the engine) looking at it from the stern of the boat.

The brass fuel pickup should be located, when looking at the rear of the boat, in the left hand corner closest to the engine. What it sounds like is happening is as you run a couple laps, the tank starts to get lower the fuel begins to slosh around. When you turn right, the fuel goes left away from where you have your pickup currently positioned in the right corner therefore causing the engine to go lean and the boat quiting. Put it in the left corner and you'll be making laps in no time.

~Mitch

 

[dwb2620]

What is your prop depth set at? Are you using a third channel fuel adjustment control? Do you have any pictures of the boat?

 

[Pete Markese]

I did re-position the brass fuel pick-up tube in the tank. It is now located in the right hand back corner of the tank (closest to the engine) looking at it from the stern of the boat.

The brass fuel pickup should be located, when looking at the rear of the boat, in the left hand corner closest to the engine. What it sounds like is happening is as you run a couple laps, the tank starts to get lower the fuel begins to slosh around. When you turn right, the fuel goes left away from where you have your pickup currently positioned in the right corner therefore causing the engine to go lean and the boat quiting. Put it in the left corner and you'll be making laps in no time.

~Mitch

Okay Mitch, I'm going to make that change tonight. I was thinking that when the boat turns to the right, that the fuel would go to the right also. I guess I was looking at that wrong. In any case, I hope that does make a difference. I do want to share however, that as much as I want this change to do the trick, I still have my doubts. The reason for that is that when this whole problem first started, I had a fuel tank with a "klunk" in it. I changed from the klunk set-up to the brass tube that's currently positioned in the right rear corner of the fuel tank. The boat died when the klunk was in the fuel tank!

Again, thanks for the thought. I'll get back to you.

 

[Pete Markese]

the new steering arms will fix it :lol: . on their way to ya.

Robin, I wish that were true!

 

[Pete Markese]

On the 3.5 the front plate will develop a hairline crack down the side of the big bearing, its a typical tolerance issue on older KB's. ALSO check the end of the drive dog where the flex shaft joins, if it cracks the motor will run until load is applied, the shaft will load against the crack, spreading the inside clearance and will bind, causing shutdown... I had a handful of these failures alone in '06, so did AFI Racing, all at National events, even at Charleston. Just throwing angles at ya. Randy

Well Randy, those are definitely some possible causes of this problem that I have NOT heard before! Interesting. Can you be a little more definitive for me on where that crack occurs in the "front plate" by the big bearing? What exactly is the "front plate" that you're referring to? Sorry for being so ignorant here, but you've got my attention; and I want to check it out.

I did install a new prop shaft assembly on this boat just a month ago, as someone else had pointed to having a problem like mine that was being caused by a bad prop shaft assembly. Anyway, the prop shaft is new.

Do get back to me on that "front plate" though. Thank you.

 

[Pete Markese]

What is your prop depth set at? Are you using a third channel fuel adjustment control? Do you have any pictures of the boat?

Currently my prop depth is set just a touch above neutral. I was told by someone else to set the prop depth at neutral and zero thrust angle. I did that. The boat shows more of an intention to get up on plane and stay there with the prop depth just a 1/16" above neutral with maybe one degree of positive thrust angle. That's where it is as we speak.

"Neutral" to me is having the prop shaft directly in line with the "ride plate". That's where the built-in water pick-up is on this hull. Another nice IW forum member showed me how to make an adjustment board so I could make more accurate prop shaft adjustments.

I am not using a 3rd channel fuel adjustment set-up with the carb.

Yes I can take all the pictures you'd like to see. Just give me an email address, as I don't know how to post them on this forum and also let me know what angles you want to see.

Thanks for being so willing to help.

 

[dwb2620]

What is your prop depth set at? Are you using a third channel fuel adjustment control? Do you have any pictures of the boat?

Currently my prop depth is set just a touch above neutral. I was told by someone else to set the prop depth at neutral and zero thrust angle. I did that. The boat shows more of an intention to get up on plane and stay there with the prop depth just a 1/16" above neutral with maybe one degree of positive thrust angle. That's where it is as we speak.

"Neutral" to me is having the prop shaft directly in line with the "ride plate". That's where the built-in water pick-up is on this hull. Another nice IW forum member showed me how to make an adjustment board so I could make more accurate prop shaft adjustments.

I am not using a 3rd channel fuel adjustment set-up with the carb.

Yes I can take all the pictures you'd like to see. Just give me an email address, as I don't know how to post them on this forum and also let me know what angles you want to see.

Thanks for being so willing to help.

I was thinking of a couple side pictures of the rear of the boat and one directly from behind the boat. I am trying to think of where I had my prop depth set at on mine. I'm thinking it was either 1/8 or 1/4 of an inch above the bottom of the center ride pad. Which I think would put it just about even with the bottom of the rear sponsons or higher. I'll pm you my email address for the pics. Shaft angle was between 1 to 2 degrees negative. Props I ran were a Prather 215 and a Octura 1740. The 215 would launch really easy. The 1740, I would have to "toss it".

As someone else mentioned, make sure your pick up tube is in the bottom left rear corner of the tank (As in the pointing towards the left rear of the boat). The end of the pressure tube should be at the upper right front corner of the tank (As in the pointing towards the right front of the boat).

Or, you can to "My Controls" at the upper right side of this page. On the left hand side is a Menu that has Invision Gallery, click on "Your Albums", and then click on "Click here to create your first album" and upload your pictures there. It is pretty self explanatory.

Thanks,

David

 

[dwb2620]

You've got mail!

David

 

[Pete Markese]

You've got mail!
David

David, I haven't forgotten about your offer to help......I am taking the pics today.

Pete

 

[Pete Markese]

You've got mail!
David

Okay David, I posted 4 pics of my Spitfire I and they're available for public viewing. These may not be the best to show my current prop depth and thrust angle, so let me know if you need better angles. If you do need additional pics, I'll get some taken right away.

Agian, thanks for the offer to help. Let me know what you see.......

Pete

 

[dwb2620]

You've got mail!
David

Okay David, I posted 4 pics of my Spitfire I and they're available for public viewing. These may not be the best to show my current prop depth and thrust angle, so let me know if you need better angles. If you do need additional pics, I'll get some taken right away.

Agian, thanks for the offer to help. Let me know what you see.......

Pete

Pete,

Are they in the User's gallery? Can you paste a link to them?

Thanks,

David

 

[Tim_Duggan]

link

 

[Grimracer]

looks way to deep to me.. Its hard to tell from the pics but I would say the motor has to go up 1/4" (5mm)

grimracer

 

[dwb2620]

looks way to deep to me.. Its hard to tell from the pics but I would say the motor has to go up 1/4" (5mm)
grimracer

Pete,

I agree with Grimracer. I would raise the motor up another 1/8 to 1/4 of an inch higher. I would even try another 1/16 to 1/8 higher than previously mentioned. The highest I would go is having the bottom of the prop shaft even with the bottom of the rear sponsons. There is no reason to go higher as that just would be overkill.

******Disclaimer: It's been about 10 years since I have ran this boat****** On my boat what I did was cut a 1/8 step on the center sponson for about 2 inches long. It seemed to settle the rear of the boat down and change the AOA of the front sponsons. So, basically it lowered the rear of the boat 1/8 of an inch. I think I still have the hull sitting up in the garage attic. If I do, I'll try to get a pick of the center sponson mod that I did. I only did this because I didn't like how high the rear of the boat was riding out of the water when on plane.

I also noticed on your engine it seems that the intake isn't radiused for a venturi effect. It's hard to tell in the pic. That might be affecting the fuel draw. On my engine, I ran the Prather exhaust throttle with a Irwin o/b pipe. All of my engines were modded by me. Mainly just a little port matching and raise the exhaust a little. Nothing major or trick.

Hope this helps,

David

 

[moparbarn]

the intake is definately not radiused. clear that thing out, pete. mine is about 1/16" at the top, contoured down to stock at the crank. remove the step/shoulder the carb sits against in there, too. don't think it's the problem, but it should help top end, when you get it sorted out. be careful at the bottom. don't change the shape/width of the opening at the crank, or the crank itself. it will affect intake (not port) timing. there may be beneficial mods in that area, but not knowing, i would leave that area alone.

dwb2620-what did you use for a header to mate to the ex. throttle? i'm assembling one now, and still puzzled on the best way to hook the prather ex. throttle to a header.

 

[dwb2620]

the intake is definately not radiused. clear that thing out, pete. mine is about 1/16" at the top, contoured down to stock at the crank. remove the step/shoulder the carb sits against in there, too. don't think it's the problem, but it should help top end, when you get it sorted out. be careful at the bottom. don't change the shape/width of the opening at the crank, or the crank itself. it will affect intake (not port) timing. there may be beneficial mods in that area, but not knowing, i would leave that area alone.dwb2620-what did you use for a header to mate to the ex. throttle? i'm assembling one now, and still puzzled on the best way to hook the prather ex. throttle to a header.

I hate to say it but, it was made from parts already had I think. If I DO remember correctly it ended up being a pretty simple setup. I'll try to dig through my old K/B outboard stuff in the next few days to see if I still have them laying around. I should still have them as I almost never get rid of engine parts. Give me a couple of days to sort it out and I will let you know. Maybe a pic or two also. All of this talk about the Prather Spitfire almost makes wish I still ran it. It was a fun boat to drive and I enjoyed beating the 20 inboard riggers from time to time.

But I moved on to the Eagle SG and Mac motors and have been happy ever since.

David

 

[moparbarn]

david, i just received an ebay motor with an old john equi pipe ("s" pipe). it had a copper fitting/ steel plate header on it. my prather ex. throttle sleeves into it perfectly. thanks for the offer, but it resolved itself when this motor arrived yesterday .

 

[dwb2620]

david, i just received an ebay motor with an old john equi pipe ("s" pipe). it had a copper fitting/ steel plate header on it. my prather ex. throttle sleeves into it perfectly. thanks for the offer, but it resolved itself when this motor arrived yesterday .

Cool! No problem, I still need to dig through that stuff anyway. The more I think about it that may be the type of header I had also. It was one of those "hey, it fits!" moments.

 

[Pete Markese]

dwb2620 & moparbarn, I'm so glad to hear that you all are now working on moparbarn's tuned pipe issue for his exhaust throttle, BUT...lets not forget who started this darn thread, and what's it's supposed to be about...as in "fixin' my darn Spitfire"! Just kidding moparbarn. You've been more than helpful, although I now don't want to start thinking about a tuned pipe on this Prather exhaust throttle set-up on this Spitfire. I don't need more variables than those with which I am already dealing.

Update on my problems...I just recently got some first hand help on the boat from a local K&B outboard engine and hydro hull expert last weekend. I'd tell you his name, but I'm not sure he'd want the publicity, although, I'm sure you know who he is. What a NICE man!

We met at a local pond and worked on the boat for hours. It didn't take him long to get the boat up and running on plane. Most of his efforts were focused purely on just dialing in the engine...needle setting, thrust angle and prop depth. BTW...your most recent suggestions to raise the prop depth were correct. We did remove the venturi carb altogether replacing it with just the speed needle set-up. I thought the venturi carb was a neat mod. He didn't! Needless to say, I was thrilled to see that darn thing circling the pond under power and not dying every other minute or so in the middle of the lake! Actually, I thought it ran pretty darn good, but my expert consultant thought it could do a lot better.

At the end of the day, he suggested I follow through with the following: (1) totally remove the cavitation plate; (2) add a 1/16" piece of marine plywood to the bottom of the center ride plate and make sure that I do not radius the sides when sanding; (3) attempt to remove the radius on the interior sponson edges; (4) replace the existing high-port piston sleeve with the newer uni-port sleeve; (5) Add some weight to move the CG forward approx. 1.5"; (6) use only 50% nitro w/16% oil blend; and lastly (7) I need to figure out some way to better seal the radio box on this old hull, as I am taking in way too much water in that critical area. He also suggested that some of my linkages could be done better as they were not as clean as he would like to see them. I should also mention that he thought the boat was pretty, but he lectured profusely that pretty isn't what it's about!

All in all, I am happy. The Spitfire is running! We hear so much today about personal exercise consultants helping those who need their advice...I'd pay a lot to have a personal rc boating consultant to assist in my on-going hobbyist frustrations. What a pleasure it was to work with someone with this level of boating expertise! No wonder he has all of those National Titles under his belt!

Again, THANKS to all of you that have offered your help on this thread. Every bit of it was appreciated. I think I can now bring this thread to a close...and good nite Mr. JM wherever you are! Out.