Johnson 235 block with 175 carbs

[Intoodeeep]

I could really use some help and advice. I have a 1978 Johnson 235 (235TXL78RJ5002998) block with johnson 175 (J175TXCCMR7824277) carburetors and electronics but NO VRO. Its a long story how this ended up this way but it is what I am stuck with now. I have just spent the last 2 years completely rebuilding my boat from the bottom up. LITERALLY!!! I have done a bunch of research and looking around but still can't find what I am looking for. I don't want to blow this motor. This motor has been rebuilt and probably has about less than an hour on it at idle trying to make sure stuff works hear and there and fixing shift cables and shift rod adjustments and so on. SO the motor has not been broke in and I haven't put it in the water yet as I am trying to sort this stuff out. I am running 100%oil now during break in. I am waiting on a replacement regulator and rectifier now so the thing will charge and the tach will work. Heres the deal. I am concerned about the carbs and the jets. I have looked into the last year johnson made the 235 which was 85 and found that the electronics are all the same except the 2 power packs which probably have something to do with RPM limiting. I know the carbs were the same except the jets. The 78 235 carbs are very different and I don't have them. I need to know how to make the 175 carbs work with this setup. Is it just as easy to use the same jets as the 1985 235 did or are the blocks between the 1978 and 1985 different? What should I do and how should I proceed? Is there anything else that I need to do to make sure this works right? Thanks

 

[194269]

Re: Johnson 235 block with 175 carbs

If my memory doesn't go south on me. Heres what I think, first of all I believe the 175 and 235 are the same displacement (meaning 149 cu/in) the 235's where 160 cu/in later in life. The port timing is more conservative on the 175 and the 175 has lower comp. ratio. The 235 carbs are 1 3/8" bore, the 200 was 1 5/16" bore and I believe the 175 carb is 1 3/16" bore. You can use the 175 carbs on the 235, but you may have to change jets, take some spark plug readings to determine that. And of course with the smaller carbs, it will not run like a 235. I have a question, what do you mean you are going to run 100% oil??? I would run the first couple of tanks at 24:1 and the rest at 32:1, I do not like 50:1 just my .03 worth. Good luck.

 

[Intoodeeep]

Re: Johnson 235 block with 175 carbs

I believe I may have meant 24:1. I am following Johnson's break in procedure. I haven't run it enough yet to take spark plug readings
yet but that will help once it is running. But the from what I found the part numbers for the 175 and 235 1985 and 1988 years for the carburetor body is the same from what it looked like. So the question remains. Do I change the jets at this point or wait and see what it does or do I start of with something different and if so what? I know it has idle air orifice, the high speed orifices and that other one what ever it is. I guess it is an intermediate but not sure. It seems to run ok at idle. But off course I have know clue about under load or high RPM yet. I know it doesn't take long to mess a 2 cylce power head up when it runs lean. As far as Horse power goes it doesn't matter. The 175 as it would be alone is more than enough let alone a 235. Like I said its a long story about why it is. But the boat was originally rated for less. I redid the displacement figures and well its ok at 175. So If IU could run it as is without messing up the motor than great. If I need to change something then thats what I am trying to figure out.

 

[194269]

Re: Johnson 235 block with 175 carbs

If the part number is the same, then I supect they are the same. I would check the parts book and see if the standard jets listed are tha same as what is in your carbs. If they ar not, then buy some. They aren't cheap though.

 

[1946Zephyr]

Re: Johnson 235 block with 175 carbs

In the top secret file here, there is a list of salvage yards and parts dealers. You should easily find what you need to make things right. A motor that new should have plenty of parts available.

 

[emdsapmgr]

Re: Johnson 235 block with 175 carbs

It's probable that the 78 235 had the large 1 3/8" throated carbs on it from the factory. Those early 235 blocks were a small bore (149 cubic inch) high port block. The 88 175 is actually a detuned 235-also a high port block- but at 160 cubic inches. That 175 came also from the factory with 1 3/8" carbs. Aside from the cubic inches difference the blocks, both are ported the same and run the same type of large-bore carbs. The big difference is in the heads. The 78 235 uses very high compression small bore heads (323872/873)-some of the best factory high compression heads made. The factory carbs in the 1978 were large (had the extra fuel pullover jet) and were jetted to flow a lot of fuel: the mains were .065. The block in the big bore 175 used low compression "bathtub" heads, so those carbs did not have to flow as much fuel to keep the pistons cool. The high speed jets in the 88 carbs are .061. You will find that the new engine will run and probably run well on the 88 carbs. My concern is that the engine may run a little lean with stock (unaltered) 175 carbs. Engines love to run lean, and you won't know it till you cook a piston. If you are familiar with jetting, I'd do a single (short) test high speed test run with the stock 175 carbs/jets. Record your top speed and rpm's. Then go up a few sizes in the mains, perhaps to .063 or .064 test run the engine, then do another test run. Record your top rpm's and top speed. Then pull your plugs and check your plugs and piston tops. You need to incrementally increase the main jet sizes till the carbs get to the point where the engine will overfuel slightly, then go down one jet size.

 

[Intoodeeep]

Re: Johnson 235 block with 175 carbs

To emdsapmgr that was very much a long the lines of what I was thinking I was going to need to do. I was just going over the specs of all of the data I have put together. The 1988 175 had idle air bleed orifices .036 in the middle and lower carb and .031 in the upper carb. Is this fine or does it need to be changed or should I be checking spark plug temps to gauge an idea? I have heard of a trick that if you have a running engine that seems to be running rough and you take a propane torch (un-lit) and put it near the suspect carb and if it smoothes out then that carb is running lean. Haven't tried it but???
Also the 1988 175 has intermediate orifices (.036) and the 1978 235 didn't have them at all. Thoughts? Is this going to be an issue at all and how might I know. I am great with small engines and those carbs and pretty good with automotive but not when it comes to jetting.
Lastly The 1988 175 had high speed jets of .061C, the 1985 175 .060C, the 1985 235 .063C and the 1978 235 .065C. As you said the 78 had 149.4cu and the others were at 160.3cu but the 78 had high compression heads. So having said all that. After taking some initial readings where would you think a good starting point for orifices would be. Is it better to start high? Also I am guessing that a good way to find if its running right would be to hit the choke but at wide open throttle. If it chokes up its right and if it gets up and goes its to lean? Same with idle right? Thank you so much for the help.

 

[emdsapmgr]

Re: Johnson 235 block with 175 carbs

Yes, there are differences in the carbs-the later carbs have a mid range jet. On your 78 235 carbs, they have a unique high speed pullover jet, which the 88 does not have. So there are differences between them. I'd concentrate on getting the issue with the high speed jets solved. Your engine will probably run just fine with the current 88 idle and mid jets. I always jet high speed jets from what is currently in the carbs (.061) and go larger, charting the changes noticed with each new jet. You need to know where you are starting from to know where be able to determine where you need to wind up. You need to go through the jetting/charting process steps to know how each jet size works compared to the others. Choking the engine is a good way to determine jetting at top end-usually works best when you have the fuel primer solenoid, which your new carbs have. I'll attach a typical charting sheet which shows my jetting logic on a 1986 150XP V6. I put 1979 200 (high port) carbs on a ported 150 (low port) block with composite reeds. Very small jetting differences will have a huge impact on top end.

 

[Intoodeeep]

Re: Johnson 235 block with 175 carbs

Thank you very much for the info. When I finish I'll let you know the results. Perhaps future people can benefit as well. I fully documented with pictures my boat rebuild/restoration project over the last 2 years. Completely gutted it and started from scratch. Also customized some areas. Will evetually publish it all when finished all the details.

 

[Intoodeeep]

Re: Johnson 235 block with 175 carbs

Ok, so its been a while. Sorry, Divorce happened. Well in October of 2011 I had completed the break in period for the engine. I wasn't happy with the compression numbers on #6 cylinder from the get go. It was within spec but not by much. After the break in period I was running it at WOT and the engine shut off. I checked everything over and it started back up and ran, all be it, it did run rough. I checked everything over and everything was fine. I suspected a faulty coil. It started up and ran smooth, so I proceeded to head back to the dock. O was several miles down river and it was about the boats sixth time out. It ran fine through the rpm range and I ran it a while at mid range and decided to see if it was just a spoof and ran it at WOT. well it ran fine for a few minutes until the connector rod in the #6 cylinder ripped from the wrist pin and created two nice sized holes in the side of the block. I did increase the jet sizes if I remember but I do remember when I did do that it ran rough and crappy. So I went back to the original and it ran fine. I was toying with the idea of going to a different prop because it didn't want to come out of the hole well. But this was do to cavitation and not engine performance. I think anyways. Its been a while so forgive me. I did end up putting a hydrofoil on the engine to help with this and it did I think. I can't completely remember, but I believe it did. I can't remember but RPM was close too. It all doesn't matter now. I still haven't looked into the old motor enough to know if it was a fuel problem or a poor build job from the guy who sold it to me. Which I think was a huge part of it.
Anyways I did happen across a brand new 1978-1979 Johnson 235 block still in the crate. I have yet to begin the rebuild but I am on the verge of finally doing so. Any recommendations or thoughts at this point before I purchase pistons and other parts that were destroyed? Most of the parts and bearings look in really good shape. I need to clean everything in kerosene and then pre oil everything on assembly. But I wanted opinions before I started.

 

[emdsapmgr]

Re: Johnson 235 block with 175 carbs

When the engine shut off the first time, that may have been due to a high speed overheat lockup. That's when the piston expands enough to lock up inside the cyl at high rpms. That can be from too little fuel/lube (running lean,) or perhaps insufficient clearance between the cyl liner and the piston to permit normal heat expansion. It's possible that the piston stuck a second time-that may be the reason that the rod blew (at just that instant.) Are you running stock (factory) pistons or an aftermarket brand? Are all of them the same manufacturer? If it's a stock block, put stock/factory pistons in it. Put the carbs back on it and test it. I test run carbs by idling to where I want to test, run for maybe 1/3 mile, note the max rpm's and exact highest speed, then chop the throttle as I put it immediately into neutral. Then pull a few plugs to read them. Chart everything on the graph, then decide on the jets to try for the next pass. Would not hurt to be running double oil till you get things sorted out. Remember these engines really run just great when they run lean-and that's the real problem.

 

[Intoodeeep]

Re: Johnson 235 block with 175 carbs

Well that would explain why it ran fine after about 20 minutes. As for the old block I have no clue what the guy that rebuilt it did. This was the second motor he sent me as the first had no compression. This one did but the numbers were low. I have them written down at home. Im a firefighter by trade and Im at work. But the numbers were all within 15psi. This guy probably screwed it from the get go. It was a bad ebay deal. Yea...I know...Im sure your rolling your eyes about now. Ok. So stock block now. Im not sure how easy it will be getting OE pistons. I looked at a few manufacturers and was considering GLM Marine pistons. I think thats the name. But I plan to go with all new pistons for investment sake and knowing what the heck is in it and not knowing what is in the other. The bad piston was pretty bad. Im sure I still have it. The other pistons looked good. So wasnt sure why the one went. So I planned to go through carbs again since its been sitting a while. I also have to pump out 20 gallons of old fuel out of the boat.

 

[jimmbo]

Re: Johnson 235 block with 175 carbs

Sounds like one cylinder went lean.

 

[emdsapmgr]

Re: Johnson 235 block with 175 carbs

It's important which pistons you use. Factory ones are a no-brainer. If you use others, depending if they are cast or forged, will have different expansion rates when warmed up. Non-factory pistons may require different piston-to-liner clearances to compensate for different expansion rates of the pistons.

 

[Intoodeeep]

Re: Johnson 235 block with 175 carbs

Ive uploaded pictures to manage attachments section but dont know how to attach them in here. The number five cylinder either had a leak or something else was going on. Not sure why one cylinder would lean out and not the other on the same carb.

 

[Intoodeeep]

Re: Johnson 235 block with 175 carbs

One more pic

 

[emdsapmgr]

Re: Johnson 235 block with 175 carbs

Thanks for the pics. Looks like you have something else going on inside the block. An internal water leak. A water leak will kill the fire in a cyl, causing it to misfire and run rough-to your earlier complaint about rough running after the first lockup. My earlier comments should be amended. You may have exploded the engine due to a hydraulic lockup. The bottom cyls are usually the ones most affected by any internal water leak. Both of yours look rusted-probably from some internal leak. While unusual, water leaks are not all that rare on the bubble backs. The location of your leak is hard to tell at this point. Looks like the seal rings on the head gaskets are intact, which would mean the water is from the exhaust system. You need to pull the inner exhaust manifold and look for any possible leak, including some possible casting porosity. I've attached a picture of an internal casting leak on an 83 inner 2.6 (235) manifold as an example. A local welder spot welded the hole and it was back running.

 

[Intoodeeep]

Ok, I figured out the photobucket thing, so here are the pictures of the majority of the motor. Hopefully it may shed some more light on the story of the failure of the engine. If not, then perhaps it will be entertaining for some. More so than it was for me at least.

http://s1255.photobucket.com/user/as...tor%20pictures

 

[Intoodeeep]

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