I have a recently completed Mini Max and acquired a Mosler CB-40 engine for it from a Canadian seller. I am now at the point of determining the condition of the used engine. With a very knowledgeable helper/guide/a&p, we got the engine fired up today after it had not run in two years. Took a little effort but got it going. The engine came to me with an Aero slide carb which I opted to change to a Zenith carburetor having checked with Scott Cassler on what to buy and I got it from him, the model number escapes me but it is what he said to get. We followed what were internet guideline on carburetor settings for main and idle and fired it up. Took a lot of tinkering with the two adjustable features and we finally got all it had with what we knew, and that was about 2800 rpm. I believe ideally we should get 3000-3200 rpm. Prop is a 54 x 22 so it was not the culprit. The other oddity is all of the rpm we could get came in the first half of the throttle travel. In the last half, we got no further rpms. Our sense of it was that we were lean and not getting enough fuel to get the rpm we should. Thoughts that come to mind are air leaks somewhere and fuel blockages somewhere. We had no luck in pursuing these possibilities. Looking for other peoples’ experiences with this engine and Zenith carb to see if we can get throttle response in the second half of travel and close to the desired rpms. Thank you very much for your time and consideration Kim Brown Hawk12979@gmail.com
I am not familiar with the Mosler engine per se, but one issue may be the propeller. The pitch and diameter may be in the recommended range but the chord of the propeller will affect the load it puts on the engine. I would ensure that the propeller chord is also correct.
That is a subject I have no experience with, I can only even guess what it means, front to back measurement of the blade at any given point, or at some specific point? Is this a subject the prop maker would know? I've ordered my share of wood props and no one ever asked anything but the numbers like, in my case, 54 x 22, one being prop length and one being, I think, the number of inches of forward progress that prop would make for every revolution. I am currently thinking my problem is mechanical within the engine and the way it is currently set up but I certainly would be interested in further discussion on the chord of the prop idea, thank you Kim Brown
It is the leading edge to trailing edge distance. I had a prop that lost a blade. It had a 2 inch chord and was made with 13 laminations and my two stroke engine turned 6500 RPM static. I sent it off to another prop shop to duplicate it "exactly". The prop I received was made with three laminations so it could not have as narrow a chord. The chord was about 3 inches. Same pitch and diameter. The engine would only turn 3500 RPM static. I finally sent it Tennessee Prop and they duplicated it exactly. Back to 6500 RPM.
Hi kfb I agree with Joe. What ever the cause, poor engine output, or such. Too much prop. You need to do some research on the size prop for your engine. Airfoil on the blade contributes a lot too. Like the one on the max wings. Thick and slow. Designed by Wayne Ison as such. Bob
Well it seemed to me that when I got the engine, the timing was set way too late, which is consistent with the story the seller told me about someone who had advanced the timing and lost three fingers from a kickback. I have been trying to make sense the way it runs while intentionally disregarding the fact that the timing is way too advanced. The guy had it set at about four degrees btdc, the coupling on the Slick mag adds fifteen to that, yielding an advance of about nineteen degrees. The Mosler manual, in a way that is confusing when some other stuff is considered, says twenty-eight degrees btdc is correct. Maybe the size of the correction I have to make, coupled with the guy's story, intimidated me a bit and made me reluctant to look at the obvious problem. I called Scott at Hummel today and he set me straight. All of his engines go out with a fifteen degree lag in the mag added to his set up of twelve to thirteen btdc, equaling the prescribed twenty-eight or so degrees. I have had a hand propped Global, a hand propped hummel, one 35 mosler, a continental 65, and now this one, i should not be gun shy about kick backs. So when we get a minute, we'll double check the timing as is, and adjust it accordingly, then again evaluate whether the prop is properly indexed or not, we may want to move it one prop bolt as we know we are going to need to be putting a bit more effort into the propping and proper positioning is important in that exercise. I am fairly confidant that will allow the engine to produce more rpms which is most of the problem we are hoping to resolve. All comments appreciated Kim Brown New Hampshire
Hi kfb Does you slick mag have an impulse coupling? If it does, it holds the mag back till about 5 deg then lets go for a hot starting spark. When running, the mag goes back to normal full advance (in your case 28 deg.). You have to set the timing on the mag after it releases the impulse, then back it up and set the timing. Bob.
So Bob... yes the Slick has an impulse coupler and your five degree reference seems to be about right for what it is when it sparks with the benefit of the coupler, but that, with a fifteen degree lag coupler, only gives you about 20 degrees btdc and it is supposed to be 28 degrees btdc when running, so I have to get the impulse assisted spark to occur at 13 degrees btdc to hit the 28 degree mark. So I have to adjust the mag so the impulse benefited spark occurs about 8 more degrees earlier than it is now for it to be sparking at about 28 without the coupler. I have adjusted the timing on a couple of Moslers and a Global all in circumstances like this, but I am having a bit of a brain cramp in the few minutes I have devoted to this one this time. With wires off the plugs, I slowly rotate the prop until it sparks, somewhere in the 4-5 degree btdc range, and then I am supposed to move the prop some amount forward, then reverse the direction of the prop far enough to start over without the impulse coupler engaging. Then the spark is supposed to be at the running spark point. I haven't managed to get clear results with that approach yet, but didn't spend much time yet either, but that is how I understand the process. Once the running spark point is established, you adjust/rotate the mag at the back of the engine to move the spark in the desired direction if need be, and then do the process again. Apparently there is a way to use a timing light while engine is running also, perhaps my engine guru guy who is coming over Saturday has the knowledge and equipment to do this. That is what I know about this. If any one wants to add to or correct my explanation, please do so, all comments appreciated Kim Brown
Today we managed to get the timing up to the correct 28 degrees btdc, started it up and ran it but were still unable to get past 2800rpm. We tried all manner of carb adjustments, none affected rpm, and all the rpms occur in the first half of the throttle travel. We do believe we are running lean more on one side than the other, plugs indicated lean and egt on one side much too high, 1400, other side 800, sensors are notorious for error but one exhaust pipe much bluer than the other and handheld laser thermometer supported the egt sensor readings. We did quick check on lifters, seemed right. Next we are going to do a valve job and lapping on the side that is running hot. We could find no explanation for running lean condition as far as any leaky intake issues. Will let you know how we do with valve work. One side note on propping when you have the timing where it is supposed to be with a CB-4 Mosler, you better put a lot of oooomph into your spin or it does indeed want to kick back and if you are not careful, the results could be ugly.
I am not familiar with the Slick mag setup on the rear of a VW (like Scott at Hummel VW's can provide). Does it operate at crankshaft RPM or camshaft RPM?
In regard to your tendency to kick back I would like to add the following for whatever its worth:
I had a 1835 VW I built up years ago and equipped it with a Vertex magneto in the original distributor hole. It turned at camshaft RPM. This magneto (Vertex has two, one with and one without advance. The P/N 704000 has the advance) has a 12 degree centrifugal advance that is "all in" by 1250 mag rpm, so 2500 engine RPM. I was dealing with the ability to advance 24 crankshaft degrees. I don't recall what I set the timing at, but based on the math there was no way I could have had it timed at 28BTDC when running AND have it spark while starting it at or after TDC. However I was able to achieve timing that caused it to run well and produce the required power and performance (RPM and temperatures) AND it started like a dream. A feeble and half hearted flick with one hand and it fired right up with no kickback tendency.
Above it was mentioned the impulse coupler gave a 15 degree lag. If that translates to 30 crankshaft degrees you should be able to time it so you get 28 or so BTDC when running and yet after TDC when starting. If you are dealing with only 15 degrees total (as in a mag intended to turn at cam rpm is being driven at crank rpm) I would expect difficulty in getting it to both run well and start well. Again, I'm not sure what your setup is but don't want to fail to contribute when someone's fingers are at risk.
Is the situation in regard to the crank, cam and mag RPM well understood? Also, can the engine be installed with the crank to cam timing (valve timing in other words) wrong which may limit your power output?
This guy modified his mag for kick back free starting if you are interested. Goes without saying to work out your current issues before making any changes with this, or any other modifications.
Newbie question, is there an electronic timing set up available for two cylinder vw types, I suppose it would be running direct off a battery and so be limited in duration?
I just printed out flydog's impulse coupling adjustment procedure and read it a few times, sounds fantastic on paper, have not had a mag out recently to look at the process in person so to speak, I couldn't tell if the pawl kickoff piece is a removable piece which would make grinding it down much easier. Sent it to my engine guru to get his thoughts, he would be the one who would adjust it if we in fact did it. It does sound like a good solution to removing some of the concern of finger/hand injuries. The man I bought this one from said someone who had been adament about maxing out the 28 degrees and even more had lost three fingers for his efforts. thanks for all comments Kim Brown
I just printed out flydog's impulse coupling adjustment procedure
Not my procedure. Just sharing something I came across on my travels around the webs. It had stuck in my memory as at one point I was considering using a magneto. In the end ended up just using the stock distributor and a total loss ignition set-up. Hand props at 0-degrees and then centrifugal advances to 28 when running. Haven't lost any fingers....yet. I prefer points over a "modern" electronic ignition module.
Lots of things could be causing reduced power but here is an easy one to check. It sounds like you are using this, or a similar carb? Remove the main jet and see if the tip is soldered shut/closed/filled. On the 1/2 VW it should be. If it is not check with Scott Cassler if it needs to be closed on the 4 cylinder. The large nut is a packing nut, just loosen that, then the needle is just threaded, keep unscrewing it 'till it comes out.
Looks good. If it was open the engine would run poorly with limited RPM's. Some aftermarket VW cam lobes have worn prematurely. Might want to measure valve lift. Compression test, or leak down test before rebuilding heads? Are you in NH?
Better to be on the 1/2vw facebook group.I once ran a 1/2vw which used to run out of throttle.That problem was solved with a fuel pump.But that was a different carb out of a suzuki Lj50 2 stroke engine.
Ace Yes I am in New Hampshire I am using a fuel pump, the lowest gph I could find Yes I also try to get advice and counsel from the Facebook groups, in nine of them, including half vws I am going to see if I can get my engine guru interested in the fly dog idea of modifying the magneto timing to allow keeping the running 28 but get the starting closer to tdc. In the box of odds and ends that came with the Mosler there is another Slick 2220, perhaps my guru guy can experiment with that one and if he likes what he can do, we would do it on the one currently in the engine. These Slicks are on ebay used for $60, also new for a little more, so even if I had to buy another one it isn't too bad. Kim Brown
When I had a 1/2 VW I used a Bosch 009 distributor ignition system. This allowed for very easy hand starts and ran well. A lightweight lithium battery will provide many hours of running time before needing charged. Reliable as heck, too.
We did a valve job on one side, the one that was reading hot based on exhaust temp, engine guru said it definitely showed it needed it and it runs better now but with new plugs we get whitish tint on elecrtode with ten minutes of run time, so we are still lean. We did a lot of air leak checking with starter fluid rather than wd-40 as some suggested, we found one possible suspect leak which will get reworked to see if it contributed to lean condition. Carb is smooth except when it transitions from low speed to high, it stumbles a bit. Using both a Tiny Tach and an expensive light reading tach, we cannot get consistent reading so we haven't been able to conclude where we are exactly on that front. Moving along slowly, will get there, if we find no significant air leak and still run lean, I suppose we have to open the carb but it is brand new from Hummel so we haven't gone there yet. Anyway, keep up the good work and comments Kim Brown
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