New M600 Carb - Issues

Jonny Quest wrote: KENO wrote: And I believe that what JQ believes is what was said earlier in this thread. KENO: At my age, remembering what I said 20 minutes ago can be a problem. This year I hid my own Easter Eggs and was stumped for hours...

Wait till you get to be my age, I'm almost as old as Pete.

I can't remember what I just remembered

We're just backing each other up on that 11 inches of vacuum being normal   

Make those eggs RED and they'll be easier to find

PS it took me 15 minutes to remember how to make those letters red.

And I believe that what JQ believes is what was said earlier in this thread.

11 inches at 8000 ft under load at idle is good.

Took her out for a spin and some carb tuning yesterday. She rips!

Dumped it in and idled around trying to get the idle screws dialed. Couldn't get above 10-11 on the vacuum gauge. Ended up about 1 1/2 turns out on both to get max idle and vacuum. Took it up to full throttle (light stumble on takeoff) and it ran up to 5,000 rpm quickly. Got about 43 MPH on the gps. About 3mph faster than it was last fall, and 1 mph faster than my Malibu is here. Pretty happy with that!

I continued to have very slight stumble on acceleration, and it would stall if I put it in gear at idle and didn't add throttle. Started messing with the screws again, but then noticed that both floats were running pretty low (I had just set them at the right level at the house before I left).   I raised both floats to where I thought they should be (just above 1/2 way up sight glass on rear, and just below 1/2 in front. I was still having the stalling issue, so I started messing with the screws. Found that RPM and vacuum were the same anywhere from 1.25 turns out to 2.25 turns out so I shot for the middle at about 1.75 turns out. I continued to have the stall issue so after some trial and error discovered I need to be at the rich end of the plateau. So I settled for roughly 2.25 turns out and it now idles well at about 900rpm, goes in to gear smoothly and settles in at 750-800rpm, and revs clean right off idle to 5,000 rpm.

I'm still getting max vacuum at idle (in gear) of about 11 . Maybe it's an elevation thing.   I'm afraid to mess with the carb any more because it seems to be running well all-around. Will be interesting to see what the plugs and the timing look like after another run.

Pretty excited about how it shook out and how easy it was to adjust the M600. Hope I can keep it dialed.

Hitting 5,000rpm pretty easily (at 8,200 feet with an acme 542) is making me think I'm going to need a prop with a lot more pitch if i bring it back to the midwest. I might even be able to run a bit more cup out here. But i like the hole shot right now.

There are lots of videos out there on how to set timing

KENO wrote: Off Trail wrote: As far as I can tell timing is a whole new realm to figure out and I don't have the tools or knowledge to mess with it yet. If I keep it here in the mountains, it will be worth figuring out though. Does this mean that you left the distributor in place during the head and manifold job and that you don't know what the timing is set at right now? If so, I think I'd get a timing light and at least check the timing to see what it is at idle and watch it advance with RPM's so you'll know initial and total advance for future reference You have a Prestolite with a clip down cap and on those full advance isn't usually in till about 4000 rpm, so don't stop checking till you're at 4000. to see your full advance. You can check the timing in neutral with no problem. The engine doesn't need to be running under load.

That is correct. I'll look into it. Wouldn't there be some outward signs of a timing issue (not running stronger than it did before the head swap, detonation etc.)?

MrMcD wrote: I believe at your altitude you can benefit from a little more timing in your engine. This adjustment can be dangerous if you happen to take this engine to low altitude and fail to adjust back to low altitude settings. I am thinking 2 degrees but maybe some with more experience at altitude can chime in. You have less air/oxygen for the engine to compress so your tune will be very unique. A supercharger or Turbo could really help at your altitude. I took my 78 Nautique up to Lake Tahoe, 6,200 ft and it only had about 2/3 it's normal power and I was modified with performance heads and more compression than stock.. I can only imagine how much 8,200 ft will hurt your performance.

I've thought about that..... But the boat may end up living at my parents place in Wisconsin...so I don't think I'll adjust timing until I make that decision. As far as I can tell timing is a whole new realm to figure out and I don't have the tools or knowledge to mess with it yet. If I keep it here in the mountains, it will be worth figuring out though.

Now you don't have to imagine.

Here's what he said last fall

Off Trail wrote: Thanks for the feedback.   Based on my experience with other boats at this elevation, I really think this thing is doing great and probably about as dialed as it could get (prop-wise) at stock horsepower (minus elevation penalty). As I mentioned, my '99 Malibu Response LX (325hp monsoon) with 600 well-maintained hours, and the perfect acme prop got that boat to 42 mph after a bunch of prop swapping, re-cupping etc. And that diamond hull was a fast hull - 49-50mph at sea level. I'm impressed the '79 will hit 40 mph.   I WILL pull the nut off and report back on what prop it has when I get the boat to my house.

Thanks to all the rest!    I'll get my float levels dialed before I go to the lake and will worry about the wedge plate if I get bored this summer.

Mounted the Alloy Marine platform mounts, and put a drain plug in the rear this afternoon....since it was snowing again and I had a nice fire going in the barn.   Might put the replacement hour meter and depth/water temp gauge in tomorrow evening.

Will get back to motor tuning when spring hits. Maybe July this year?

Did you change your jet sizes to match the altitude? I've had 2 QuickFuel carbs running at 4,400+ feet of elevation in the Salt Lake City area. Both carbs ran rich with the stock jet settings (sea-level is stock). I went 2 sizes smaller for jets in both the primary and secondary metering blocks. That solved the "too rich" condition.

Checking the float level is critical -- as mentioned above. the QF carbs should come from the factory with pre-set float levels, but my M-650 came from the factory with the secondary float out of adjustment -- waaaay too high of fuel level in the bowl. The only real problem I've had with QF is that the primary bowl needle/seat assembly had a small piece of brass / metal shaving that somehow became lodged and prevented the needle from closing. QF sent me a needle/seat assembly. Super easy fix. No problems since, only high performance.

JQ

KENO wrote: Duane's kinda like a mad scientist. He was too cheap to buy some raw water pump parts, so he got a big ol' chunk of metal and made them himself

Aw come on Ken, which pump???

You will have no problem running that carb without a wedge plate. Edelbrock/Carter style carbs are much more sensitive to angle of the engine.

On a 4160 style carb you run the front bowl pretty low and the rear bowl a little higher than normal to compensate for the rearward angle. While a wedge may be the best possible setup for a carb to be level it's certainly not necessary.

Get the bowls adjusted exactly where you want them before messing around much with idle settings. The rear has no idle settings and differences in bowl level will cause slight idle changes.

KENO wrote: If the rear bowl is overflowing or seems high , I'd adjust that too

What a novel idea, a separate adjustment for the rear bowl. How did I miss that??    I swear I looked, but it was partially hidden under the spark arrestor and I didn't give it another thought.

This is becoming the 'stupid questions about carbs by a newb' thread. Sorry.

For "Optimum" performance the carb should be level as poss. With all your plates under the carb it seems as though you should get it a little more level with some work.

First pic shows my wedge plate. Pic #2 shows the carb level and the engine at normal angle.
You are going to really like the QF/Holley carb.
ps.   Follow KENO's directions. He will steer you straight!

Very good to hear you have it sorted and running!

Off Trail wrote: My plan is to just tune the idle screws to max vacuum at idle - as long as it is somewhere in the teen's I should be good.

Consider this idle mix procedure - set for max vacuum when in gear and in the water for best results, else it will be on the too-lean side and be a little dull off-idle, plus other issues will manifest.

After this it will be an off-idle beast with lots of snap, no hesitation.
This will also provide best conditions for no-throttle starting

This simulates the auto-trans carb setup procedure (in gear - wheels chocked) of yesteryears.

Will also minimize the delta-rpm   from in-gear to out-of-gear because your are setting for best idle torque, not just raw rpm

As far as vacuum readings, put the gauge on your Malibu to get an idea what would be a good reading to be looking for.

You'd figure it should be pretty close to that reading