Running issues with Johnson Venom 200

[96Javelin409]

Let me start by saying sorry for the long post but I like to give anybody willing to help me with anything as much info as I possibly can. I'm having an issue with a rough idle and poor hole shot with my J200STLEOA on my 96 Javelin 409. The only real repair history I know of is that the previous owner had replaced the VRO pump with a conventional style pump and went to premix and I rebuilt the carbs with OEM kits 3 years or so ago when I bought the boat for no real reason other than I had no idea the last time it was done and the previous owner couldn't remember. Also replaced the stator when I first got the boat with a CDI brand unit as I noticed it had the physical leakage they seem to get and also the charging circuit wasn't working correctly which replacing the stator fixed.

I work on modern cars for a living so I have a lot of diagnostic equipment to try and figure out this issue but I'll be the first to admit my experience with 2 strokes and also older engines/fuel injection is limited (custom tune on my 95 tbi chevy being about the oldest thing I have experience with). I have a hard copy factory service manual I got off ebay but am curious if there are any common failure points or any quick diagnostic methods someone may be willing to share to help speed the up the diagnostic process. I am the type of person that likes to really dig into an issue and prove a failure point and not guess at what the problem may be or throw parts at something.

Having said all that the first issue I'm experiencing is a rough idle/misfire at all times except for very randomly the engine will idle extremely smooth for a few seconds then go back to rough again. For initial diagnostics for the idle issue I have done a cylinder contribution test and all cylinders seem to be contributing evenly. After that I performed a compression test with 110psi on all cylinders (is this low?). After doing those 2 tests the engine had been running on the muffs a while and was getting pretty warm so I stopped and this was the last time I messed with the idle issue. Now typically for a rough idle/misfire issue on the cars I work on I will hook my scope up to the crankshaft sensor signal wire and trigger another channel off of an ignition coil to have a reference for which cylinder the crankshaft speed is dropping on to discover a misfire but I'm not sure if this is do able on this setup, I'm not sure what I could trigger off of for crank speed.

My next issue is a bog/stall during hole shot. I haven't spent a great deal of time on this because I'm thinking the issue at idle is probably contributing to this. I did do a link and sync as outlined in the factory manual which didn't have any effect. One thing I've noticed is that during the first hole shot of the day the engine will only reach about 2000 rpm or so and then if I stop and put it in neutral and rev to about 3000 rpm a couple times and wait for the engine to return to idle the hole shot will be pretty normal though still a little sluggish. My 2 theories on this are either the engine is running very rich at idle and revving it burns off some excess fuel or there is an air leak somewhere and revving the engine helps remove the air and prime the system, once again just guesses, no real data to back this up.

The engine just started doing this one day, there wasn't any rhyme or reason for it. Also one other question I have as far as the bog/stall on the hole shot, is there any way to run an o2 sensor so I can actually verify whether the issue is not enough fuel or too much fuel causing it to flood out (pushing key in to engage primer solenoid makes the problem worse so I assume it's not lack of fuel delivery)? I'm use to being able to pop into live data and quickly figuring out whether a car has poor acceleration due to a fuel delivery problem. Once again sorry for the extremely long post, thanks for any help!

[96Javelin409]

That is way too hard to read. Break it up into a couple of paragraphs and it will be so much easier to help you.

Fixed that

[bigbore]

It’s got idle adjustment screws/at the top left corner of carburetor start with half a turn in (at idle) (on each cylinder)n if it’s worse go full turn out-counter clockwise- n see if that fixes your idle issues.
also I’ve good luck removing vro n running a Holley red fuel pump/mounted as low as possible next to fuel tank n to motor from there.just take primmer ball out n check valve out tank-spout/run straight 3/8’s fuel line to front side of filter in engine compartment n put 40:1 or 50:1 pre-mix fuel in tank n run it.

[96Javelin409]

I had issues with a rough idle and what seems like a miss at idle or a lean sneeze. New reeds with a good lap on the cages fixed that.

It is worth the time it takes to check your fuel line for leaks. Disconnect it at the pump and tank, plug one end, and then draw a vacuum on the other end. I found bad primer bulbs like this before. They did not leak, but were letting air in the system which is no good.

I will definitely be doing that test on the fuel line that's a great test. Is there any particular brand of reeds to look for?

[96Javelin409]

It’s got idle adjustment screws/at the top left corner of carburetor start with half a turn in (at idle) (on each cylinder)n if it’s worse go full turn out-counter clockwise- n see if that fixes your idle issues.
also I’ve good luck removing vro n running a Holley red fuel pump/mounted as low as possible next to fuel tank n to motor from there.just take primmer ball out n run straight 3/8’s fuel line to front side of filter in engine compartment n put 40:1 or 50:1 pre-mix fuel in tank n run it.

I'll definitely do those idle screw adjustments. If it is actually running out of fuel on the hole shot I'll look into that fuel pump. I'm off labor day week and don't really have any plans so I think I'm going to fiddle with these issues and hopefully have it figured out by the end of the week.

[bigbore]

Yea removing vro not a bad idea for a cpl. Reasons/just remove n plug pulse limiter from bottom of front case half.Holley red/or edlebrock red will do the job.

[96Javelin409]

Hey guys sorry this thread died a bit, ended up with a few extra projects heading into winter than I had planned and the boat kind of got put on the back burner. I did manage to figure out the low rpm/poor hole shot in the morning issue. Apparently when I replaced the stator due to the charging portion not working when I got the boat, I didn't get all of the old melted epoxy or varnish or whatever seeps off them when they burn up, out. I'm thinking what was happening is the epoxy would be hard in the morning and keep the timing arm from pulling forward and advancing, then after the engine warmed up the epoxy would free up some and the arm would be able to move. I took the boat back out twice after just doing this thorough cleaning and the issue never showed up again so I'm pretty confident in that fix since it was happening every time I took the boat out before.

I did put some Chris Carson reeds in it which wasn't a bad job at all. Can't say I noticed any kind of crazy performance changes but did notice the engine seems to run a little smoother at idle and at speed and slightly better throttle response. Didn't get a chance to take the boat out enough to see if it helped with fuel economy. I did find I was running out of fuel on the hole shot so maybe that's an indicator there's some more air coming in anyways. An easy workaround on the fly was for me to just push the key in to prime for a second before I took off. I looked in my factory manual and got some part numbers for intermediate air bleeds and was able to track a set 3 sizes down and 4 sizes down on ebay and installed the 3 size down ones and that's about where I made it to. Unless we happen to get a random warm weekend day I'll have to find out how much that helps in the spring.