Need Help with 170 boat motor!

I have been having problems with my 64 Correct Craft boat with a 170 inboard motor,not wanting to turn over 2200 rpm's under load. Here's a little history:

Last May I installed a "new" head. It was from a 1979 200. I had the head rebuilt. it was milled .060, new valves and springs were installed. I cleaned up the rough castings in the combustion chambers and port matched the aluminum exhaust manifold. I had to make a SS elbow to adapt the Carter YH sidedraft carb. This Elbow has a 1 3/4" IS dia. to match the intake hole. (The original only had a 1 3/8" hole... it also let the carb bowl hit the larger intake runner of the 200 head.

When I got the motor back togeter, it ran great in the driveway, cooled by a garden hose. It will rev up to redline no problem. The first time I took it out, it fell flat on its face around 2200 R's.

To date heres some of what I've tried..

Rebuilt Carb.
Rebuilt mechanical fuel pump.
All new fuel lines.
Added spin on type fuel filter.
Replaced Mallory dizzy from another motor.
New points, cap, condenser, rotor.
Changed ignition coil (from another motor)
New steel exhaust pipes.

Motor idles with around 17 to 18" of vacuum.
Set timing at 10BTDC per manual(as well as 10 to 15 more/less each way)
Dont know total advance, but with light it moves when throttle is cracked.

I have run an electric fuel pump "plumbed" into a 5 gal gas can
and running directly to the carb, completely eliminating the boats fuel system ...still no go.


Thoughts?


btw hers a pic of the motor...

I would say you just don't have enough compression. The 170 heads have about 10 to 12 CC less in the combustion chamber than a 200 head would. A 64 170 would have also used a steel shim head gasket too if you’re now using a composite head gasket than the .050 mill would only cover that difference in volume. So if you’re not using a popup type pistion to help get it back up than you’re giving away a lot of compression that it once had.

Is there a choke on the carb?

That is one of the reasons for rebuilding this head.... When I bought the boat, the PO had put a 1973 head on it. That head also had developed a crack in the intake. When I took the 73 head off, it still had 62cc chambers and a Victor gasket. We figured that setup had somewhere around 7:i compression. but, we had run that for 5 years.

The replacement head's combustion chambers CC'd around 50 1/2 after machining. We left a little for decking the block, if ever rebuilding the bottom end. With the Felpro head gasket, I think this figured out around 8.3:1 or so. However, I have noticed a little "smoke" coming out of the valve cover vent tube, so I did pull a compression test on the motor earlier. (very old "Hawk" tester ...not sure of accuracy) With no spark plugs, cold, it ran between 130 and 140. (The manual calls for 160 +/- 20) I then squirted a little 30 wt oil in each cylinder, evreyone went up at least 20 lbs to 25lbs. So, there appears to be some weak rings? But the 17 to 18"hg at idle isnt too bad?

JackFish":3eystig6 said:

Is there a choke on the carb?

Click to expand...

Yes, but the spring in the choke housing is wound to keep it opened all the way.

Are you saying that it will not rev to redline in neutral?
Or is that in gear?

First, that exhaust manifold looks sexy all polished up!

Since you moved the carb a little bit did you confirm WOT? I took a look at one of your old threads and it looks like it had the same red throttle cable?

It will rap up to redline in neutral... I can hold it pretty much where I want in neutral. Iv'e held it around 3500 for 4 or 5 seconds , no problem.

When I put a load on it , in gear, is when it stumbles. It will actually stumble if you push the pedal past aprox 1/2 to 5/8 throttle, even off idle. That happens to be in that 2200 range when trying to plane.

The motor is timed at 10 BTDC. I dont have a dial back light. so I dont know total advance, but when I give it a quick shot of gas in neutral, the timing mark advances smoothly, I'm guessing 20 or so more degrees. We even tried turning the dizzy while underway... still stumbled.

'68falconohio":fd9fwuby said:

First, that exhaust manifold looks sexy all polished up!

Since you moved the carb a little bit did you confirm WOT? I took a look at one of your old threads and it looks like it had the same red throttle cable?

Click to expand...

Thanks ....I spent a "few hours" on the manifold... When I made the SS carb adapter and polished that, I thought polishing the manifold would really make it look good. Doesnt run worth a cr@p, but looks good!

It is a different cable, but, when I moved the carb, I had to make new brackets for the gas pedal and the cable mounts to get full throw on the carb lnkage. Still have a little work on that...I cant get it adjusted to idle slower than around a 1,000 R's, but it opens all the way.


FWIW, here is a "before" pic that also shows the original carb adapter elbow.




and a pic while mocking the adapter up ....

Would be better to do the compression test when it is warmed up, but should be good enough to run decent. How is color of plugs?

64 inboard":aqq41kt0 said:

.......
When I put a load on it , in gear, is when it stumbles. It will actually stumble if you push the pedal past aprox 1/2 to 5/8 throttle, even off idle.......
... still stumbled.

Click to expand...

Poor compression won't make it "stumble". It would certainly make it weak but the stated "stumble" indicates a fuel delivery or ignition problem.
Joe

I agree with the ignition or fuel delivery, but have pretty much done evreything I can think of to eliminate the obvious. I have changed dizzys from another 200 marine motor. We tried rotating the dizzy while underway, no difference, this should eliminate all timing advance situations? New points, cap, rotor, condensor. Changed coils from another motor.

The plugs are burning kind of funky, but with the condition, never gets a good burn going? Most of the plugs are whitish on one side and tan/brown on the other... almost like which valve its oriented towards? Number 3 is black on the one side, while tan on the other.. Here are some pics.. I rotated hat plug so you can see what I mean...







FWIW, I just got some new 45's to try in it .


.

Did you use the same cam and timing chain set? If its not the same did you degree it? Just wondering if its a cam timing issue. Not sure about the little fords but on other engines I have seen up to a 10* difference in cam timing from what its supposed to be (even when I install it correctly which is not all the time).

What type of distributor do you have? A pictue or two of it would not hurt. Where does it get it's advance signal from? Lack of advance should not make it fall on it's face, but at higher rpm's initial advance would only get you so far, then it would accelerate more slowly.

EDIT:woops! just saw the caption that it's a picture "while mocking up the adapter" so can diregard following silly question
Silly question, but I assume that's the old carb mount to the intake manifold next to the new SS hookup? That's sealed real well right, otherwise potential for major vacuum leak

The half & half condition of the plugs makes me think maybe you're leaning out at higher rpms
EDIT2: Float level too low??
Good luck!

PS Is the odd hat looking thing on the stern side of the carb some type of air breather/filter?...just curious

Looks like trouble on #3 & #4 is there away you can mount the old carb adapter back on and try it? Maybe make a 1/4 to 1/2 spacer at head mounting to raise it up enough to clear. Or could you use a car type carb like a Carter bolted straight to manifold just to see if it would pull better?

If that is a stock head, you have a hollow passage at the 3 and 4 port where the heated air for the choke pulloff spring is drawn. These tend to burn through and create either/or an exhaust leak or an intake leak. Most likely an exhaust leak INTO the intake. That is one thing that will influence the 3 n' 4 port. Then there is the intake port divider, which might be of some use here in separating the intake streams.

And are you getting spark advance under load?

More than that, I got nothing.

I did not touch the cam. I am planning to see if I can degree it sometime this week. The boat never has run great...but I always attributed it to the wrong head. ...and it would run at least 3200 to 3400 depending on props.

The dizzy is a Mallory Marine unit. No vacuum advance ..mechanical only. I think the adavnce is working ok... like I said before, I had a friend actually rotate the dizzy back and forth, made no difference. here is a pic of the dizzy when I had the head torn off earlier this spring..


A few of you might remember from earlier posts...this would not run any temp when running it before...hardly move gauge off 100 degrees.


Yes, that is the old adapter setting next to the SS one I made. We have adjusted float level from a strong 5/8" to 1/2" ...manual says 9/16". At the same time we tried rotating the dizzy, we squirted gas in carb also when it was stumbling...made it worse. But then again, all we did was drill an 1/8" hole in a fuel inj cleaner bottle cap... all we had at the time.



the odd hat thing is probably the flame arrestor...it also has a 1/8" copper line running from an overflow, back to the intake manifold right below the mount base. If the carb floods, this is supposed to pull the raw gas back into the engine. heres a lttle better pic of the arrestor.

bubba, before I put the engine cover back on,I had thought about trying a regular carb at one time, but I didnt have one to try. Is there a particular reason you are looking for, by trying to adapt the original adapter elbow back on the intake? an adapter could be done with some machining, but I decided to go this route because of one less gasket required. Plus the original adapter only has a 1 3/8" hole at the intake....The SS homemade one is 1 3/4" all the way...same as the intakes opening.

ludwig, the head is a stock head ...Where would the burn thru hole be located? between the intake and exhaust ports? Would I have noticed it when I was cleaning the head up? or is it inside where it cant be seen easily? Should the machinist have caught that?

bubba, before I put the engine cover back on,I had thought about trying a regular carb at one time, but I didnt have one to try. Is there a particular reason you are looking for, by trying to adapt the original adapter elbow back on the intake? an adapter could be done with some machining, but I decided to go this route because of one less gasket required. Plus the original adapter only has a 1 3/8" hole at the intake....The SS homemade one is 1 3/4" all the way...same as the intakes opening.

Click to expand...

Hard to tell without seeing and hearing what its doing, though I do believe that its nothing in the distributor or the ignition parts these were a very good system and as you have already verified that it is advancing. Little else you could change except maybe to add a CD box that would be of any more improvement. So am focusing in more on the carb now just from the condition of plugs, is just a guess as I have not seen a one of these carb’s apart or even a blown up of its parts diagram before. But I am wondering if the adapter is maybe messing with the carb’s venture signal. Thinking there is a reason that they made it with a smaller inlet and with most everything else stock parts i.e. cam and short block, sometimes bigger isn’t always better.

A quick history on the Carter Yh carb.. ..
It was used in the late 50's / early 60's by various engine marinizers because of the low profile, aiding in engine cover clearances. One of my boats is powered by a 327 AMC/Hudson motor that has two of these carbs. The carb was used on turbo charged Corvairs, as well as "tri-powered" on the early six banger Corvettes. One thing kind of different is the fact the engine has to be cranking before the carb will pump fuel into the throat, a saftey factor to help keep from flooding raw gas out of the throat.

As for the adapter size, I questioned that early in this process. The guy that rebuilt the carb, and actuallly helped author a book on these carbs, has seen pics of the setup. He does not believe the elbow is an issue at all. All the velocity of the carb is in the throat of the carb body itself. He did not like the way the carb is mounted" backwards" on the motor.... with the accelerator pump in the highes part of the bowl, but doesnt think that is the problem either. Like I told him, they all ran that way since 1963. He said, the larger dia would help in fuel flow at higher rpm's(if I ever get to that) and could possibly change throttle repsonse, but probably not enough to notice.


I'm wondering about the cam timing...as well as the "burn thru hole" mentioned before? As for the plugs, is the fact of the stumble cause for their wierd colors?