1975 75hp Chrysler Carburetor question

[bsas2]

Hi All,

I am located in Australia & trying to resurrect an old 757HA, & so far so good. Pretty good nick considering the age. It has been sitting in the previous owners's back yard for years, & the carburetors are all gummed up. I have stripped them down, but there are a few things that don't appear correct. I was wondering if someone has an exploded diagram of the Tillotson WB22A Carbs that are on the motor, for a bit of a guide? The air idle screws have an "o" ring on them but I thought there should have been a washer between it & the spring. As it is now, the spring sits against the rubber ring. Surely this isn't correct. Would also be very appreciative of anything else I should look out for, thanks & hope to hear from someone soon.

PS Already found a wealth of invaluable information on the site, so it is a credit to all the contributors. Well done.

John.

 

[jerryjerry05]

Re: 1975 75hp Chrysler Carburetor question

It's not an idle screw,it's an air/fuel mix screw for low speed operation.
The idle is adjusted with the towershaft.
Parts diagram doesn't show an o-ring or a washer.
Just the screw and spring.
Possible someone's messed with it?
The screw, is it smooth all the way to the tip?
If it's not it needs a new one.
Being in Au.It's gonna be expensive to get parts so be careful when doing anything.
The rebuild kits are NLA unless you find one on a shelf somewhere.

 

[Frank Acampora]

Re: 1975 75hp Chrysler Carburetor question

OK! Here's the deal: I don't know of any WB carbs of that age that had an O-ring seal for the low speed idle needle. It sounds like the P.O. saw an OMC and decided that he liked it OR the threaded body of the carb is so worn that he had an air leak. You can use the O-ring or not, It certainly would not hurt anything. HOWEVER: Using an O-ring and washer MAY take up all the slack in the spring, leaving no adjustment on the needle--it was never designed for that.

All WB carbs are essentially alike except for the high speed jet so parts from one are swappable into another. IF you can find a set of three for a reasonable price you can use carbs off another 75Chrysler, an 85, or even a 90 Force. Just don't expect any more power because the 75 has much smaller exhaust ports and THAT is what limits the horsepower.

 

[bsas2]

Re: 1975 75hp Chrysler Carburetor question

Hi Guys,
Thanks heaps for your help. I thought it seemed a little cramped with the "o" ring & washer, so that makes sense. Thanks again for the prompt responses.
John.

 

[Sea Stomper]

Re: 1975 75hp Chrysler Carburetor question

Just don't expect any more power because the 75 has much smaller exhaust ports and THAT is what limits the horsepower.

When I compared my 75 carbs to my 85 carbs, I could swear that the 85 throat was bigger in diameter than the 75 and I thought that might affect the power output also. Having said that, I've been running an 85 carb in the middle position on my 75 for about 550 hours over the past 5 years in the ocean, runs perfect. My piston heads and cylinder walls are perfect also, never run it above 4000 revs.

Interesting about the exhaust port size, I didn't know that.

 

[Frank Acampora]

Re: 1975 75hp Chrysler Carburetor question

Bore and stroke on the Chrysler 70, 75, 85, and 90 are all the same. ( Force 70 and 75 are completely different animals) Thus, due to expected airflow, carbs from any engine can be used on any other engine.

However, it is aesthetically displeasing to me to mix and match carbs on the same engine. Thus, I simply would never use, for example, two 75 HP carbs and one 85 HP carb.

The 75 has circular exhaust ports while the 85 has vertically elongated exhaust ports with greater area. This engine has less exhaust restriction and scavenges more exhaust from the cylinder. This allows a cleaner, less diluted intake charge from the bypass ports and lets the engine develop more power. The larger carb allows the engine to pump more air, taking advantage of the better scavenging. This engine is also rated for 85 at a higher RPM than the 75. 75 carbs have a 1 3/16 venturi diameter while the 85 carbs have a 1 5/16 venturi diameter. In addition, the butterflies on the 85 carbs are slightly larger than the butterflies on the 75 carbs, again, for less airflow restriction.

 

[Sea Stomper]

Re: 1975 75hp Chrysler Carburetor question

Very good. Yea, any sensible person would not mix carbs. But I did it while troubleshooting a plug fouling issue at the same time that I Frankenstiened a Mopar ignition box and a very energetic MSD Blaster2 coil ignition system onto this thing, the latter of which was the best thing I ever did to it, along with running L86C plugs. I did some strange things with the electronic distributor to time it in correctly since the firing logic of the Mopar box is opposite the CDI unit. The optical pre-amp interrupter triggers the Mopar box nicely. I"m not going to post how I made it work due to the probability that someone will try it and blame me for their burned up pistons. I will just say that the 3 cylinder electronic distributor is perfectly set up for opposite logic triggering of the Mopar unit with some minor hacking and major timing corrections.

I pull my cylinder head once each mid season to inspect the piston crowns and they still look like new but I keep my revs under 4000. I occasionally bore scope the cylinders also but I like pulling the head better.

The circuit was pulled from a Kawasaki 750 3 cylinder motorcycle engine modification I found on the internet where the guy wired in a Mopar box triggered by the Kawasaki's interrupter. The distributor mod was my creation. Mopar boxes are cheap, you can get them for under 20 bucks and they are good coil firing units. Also, I'm able to run any automotive tach with this setup on the 6 cylinder position since a 6 cylinder 4 stroke and a 3 cylinder 2 stroke have the same number of firing events per one revolution of the crankshaft.

Corrosion is not too bad for 6 years of salt water operating. That's another great thing about these Chryslers. With religious fresh water flushing immediately after boat retrieval, they take salt water operation very well.

The engine in operation

These experiments like this come from 40 years as a professional wrench, being a marine diesel tech working for Cummins, and I can be a bit outside the box doing engine work (I can burn up pistons with the best of 'em! LOL). I can monitor things closely to know when things start going wrong, and this thing has been absolutely amazing for reliability and total trustworthiness in the Pacific Northwest ocean environment. It's a 1975 75 horse Chrysler just like the OP has. After 550 ocean hours I think I'm sticking with this engine model until I'm too old to do this anymore. I was going to repower with a 4 stroke but the more I use this engine and the low cost of operating it, it just doesn't make sense to spend thousands on a repower.

Anyway, I never did put the 75 carb back on the #2 hole. This thing has been flawlessy reliable. By the way, the plug fouling issue happened when I was trying out Pennzoil 2 stroke oil at the same time I modified the ignition system, and put that carb on during troubleshooting. The Pennzoil just didn't burn right, it just gummed up the plugs. I went back to Valvoline which works perfectly and so does the johnson evinrude stuff. The L86C plugs are really a nice match to the MSD coil but man they put out some hellacious ignition noise (non resistor plugs). Cuts my VHF receive range down a bit but I really don't care. I get 3 seasons out of a set of plugs with this combo without fouling once, about 150 hours or more. So the moral of the story is that as insane as the above configuration is, the results over 6 ocean fishing seasons are good with no failures or hardware deterioration of any sort over a 550 hour span. If I ran at WOT which I never do, the story might be different. Ocean running at high speeds often results in going airborne and I don't like that.

I like your posts Frank and they are a totally valuable resource.

Anyway bsas2, Frank is the supreme expert on these engines and you can't go wrong following his recommendations. Don't do anything I do because I am just too independently experimental, and experiments like mine can lead to disaster. I've been following Frank's posts for years and they have some really great stuff in them.

Robert Reed

 

[MickLovin]

Re: 1975 75hp Chrysler Carburetor question

I have a 757HC 1976 model and another 75hp which was 758HOB it is a 1980 model, they had different size jets but not by much one was .066 and one was .072, If you need any help in australia, I have a spare set of carbies which I have kept for parts if you need.

 

[MickLovin]

Re: 1975 75hp Chrysler Carburetor question

I also have a spare 75HP motor