All NEW Parts, 1 annoying miss HELP

I'll try to keep this as short as possible. I've never had to chase a miss on a modified, so I am trying to figure out the cheapest way to figure out my issue:

Brand new 602 crate motor. New Carb, Ron's piston fuel pump, regulator, and msd rev box. I sent the new distributor to TRC and they wired up the rev box, locked it, and put a stronger coil in it.

I put a mark on the balancer for 32 degrees and lined that up to 0 on the timing pointer so it would start up close to what I was shooting for. Once I got it started, a buddy was running the timing light while I turned the distributor and held the throttle. My mistake was that I used the same color paint for 32 degrees and TDC on the balancer. We set the timing to 32 with the light off the 32 degree mark on the balancer and ran it for 15 minutes or so. The motor didn't sound how I wanted and there was a miss at idle. I could hold the timing light up to my hand and the flash would miss when the motor changed tone. Also, every once in awhile, the light would only come on for a couple seconds at a time, then off, then back on.

Shut it off and called TRC. We talked and I mentioned the 64 degrees. He said I could have blistered the plugs and need to change them out. I put a new set in AND changed the color of my marks on the balancer and it seemed to clear it up at idle. There was still a miss at 2500 to 3000 rpms. With the timing light the motor would read 0 on the pointer and 32 on my light, but every few revolutions the TDC mark would appear lower on the motor like at the 3 oclock position...then back to 0.

I worked on other things and just before heading to the track I wanted to check it out again. I started the motor and it sounded odd. Ran it for 2 minutes or so thinking it was really cold out. Still missing so I pulled the breather out and fuel was pouring out of the front vent tube. Tapped on the needle and seat and it finally quit. Motor sounded good, but now the miss was at idle again. Every few revolutions, 3 oclock again on the TDC mark. I lowered the bowls a little because I thought it was a little high.

Called TRC and they said clean the plugs real good or get another set. Clean the bowls out just in case hose dust got in there causing the needle not to seat. I did that all that and still has the miss. I'm going to change the distributor out tonight with a DUI setup.

It really seems electrical with the weird intermittent timing light flash for awhile, then the missing and TDC coming in at 3 oclock. I just don't know what to check and really can't afford to spend a bunch of money troubleshooting. Any ideas?

It does sound electrical. I would make sure the engine has a good ground, and also make sure you have a good consistant 12v signal to the distributor with the engine running.

I would also unkhook the MSD rev limiter and see if it does it then.

If swaping out the dist with the DUI solves the problem it may be the coil they swapped out in the original dist.

Eric

un plug the soft touch, unplug your tach. See how it sounds, but I also had an engine do this with MSD box and dizzy,the purple and green wire for the pick up in the dizzy was phased wrong. So I had to put the wires purple to green in the little black connector next to the box instead of green green purple purple.It fits tight but it will go when pushed hard enough. This fixed the erratic timing pointer issue and cleaned up the missing and hesitation. I have run into this 3 times over the years with MSD. Im not sure why it happens but it does every now and then

The way the company wired up the rev box, it appears as though it will not fire with it unplugged. I turned it over for about 10 seconds or more and nothing. Waiting to hear back from them on that.

I tried a DUI distributor last night and it sounded much better all the way up to about 3200 rpms. At that point, there is no erratic timing pointer movement, but I can hear small stumbles if I hold it at a steady rpm. It seems like if I were to drive it, I would feel surges in the seat. I don't want to rev it too high without a load, but I also want to make sure I don't have a bad miss while racing. I plan to take it on the road tomorrow so it will have a load.

After the DUI, I put the new distributor back in (it is locked like the DUI). This distributor seems to allow the timing to move around much more. I set it to 32 at 1500 rpms and by the time I got ot 3000 rpms it had advanced almost 8 degrees. Doing it this way caused the miss again. I tried lowering the timing at idle to see what would happen. Set it at 25 at idle and at high rpm, it was right at 32, no jumping around this time, but I could hear the same stumbles that I did with the DUI. If I ran the timing back up just a little at idle and start to rev, I get the bouncing of the timing again...most revolutions would hit 0 on the pointer, then down about 3 oclock on the balancer and over and over again.

Any more thoughts after this research?

Quote:

---

Originally Posted by dluna11w

The way the company wired up the rev box, it appears as though it will not fire with it unplugged. I turned it over for about 10 seconds or more and nothing. Waiting to hear back from them on that.

I tried a DUI distributor last night and it sounded much better all the way up to about 3200 rpms. At that point, there is no erratic timing pointer movement, but I can hear small stumbles if I hold it at a steady rpm. It seems like if I were to drive it, I would feel surges in the seat. I don't want to rev it too high without a load, but I also want to make sure I don't have a bad miss while racing. I plan to take it on the road tomorrow so it will have a load.

After the DUI, I put the new distributor back in (it is locked like the DUI). This distributor seems to allow the timing to move around much more. I set it to 32 at 1500 rpms and by the time I got ot 3000 rpms it had advanced almost 8 degrees. Doing it this way caused the miss again. I tried lowering the timing at idle to see what would happen. Set it at 25 at idle and at high rpm, it was right at 32, no jumping around this time, but I could hear the same stumbles that I did with the DUI. If I ran the timing back up just a little at idle and start to rev, I get the bouncing of the timing again...most revolutions would hit 0 on the pointer, then down about 3 oclock on the balancer and over and over again.

Any more thoughts after this research?

---

I don't have much to add, but I do have a question. When you ran it on the DUI, did you have the intermittent timing light flashing? You said it still had a stumble, but that could be something as simple as plugs starting to foul. You may be on to something by running the DUI.

The original weird timing light flashing where it would just flash at random is gone with both distributors. The DUI didn't jump around at all even when running it up to 3500 rpms.
The new distributor only jumps around and TDC hits the 3 oclock position every once in awhile if I increase the timing to 32 to 34. If I keep the timing lower, it doesn't happen.

It did dump a bunch of fuel in it at one point and I thought it might have fouled a plug, but it sounds really good right now until about 3500 rpms. Then comes the slight stumbles. I don't mind changing plugs again, but I really don't want to dump another $30 at it if it isn't going to do much.

THANKS for the replies!!!

I know what you mean. I had a stumble at idle up until about 3000, and then it would clear up. My car has always ran fine like this. But it does appear yours might not be just plugs. Especially that its not doing it with less timing.

It sounds like your cam might be walking and causing the static timing.

have you check the play in the dist. that is having the erratic issues?

Is this car an IMCA sport mod? If the MSD soft touch is wiried in correctly you should be able to just unplug the wiring at the distributor and everything should work as normal.

If you still have the MSD instructions there is two different ways to wire up an HEI. I run a 602 crate with the original untoched distributor and a MSD softtouch. I dont even use the purple wire coming from the box. All of my wiring is connected outside the dist, Not inside on the pick-up coil. This set-up works perfect and the limiting is not harsh.

I wouldnt worry too much about slight running issues just reving the car at 3000+ rpm, You really need the engine up to temp and a load on the engine. Eric

Hey c10, you may want to go to the MSD website or look at the wiring instructions that come with a new box or distributor. Correctly wired, green to purple and purple to green. I know it seems backwards but green NEVER goes to green or purple to purple.
On the subject at hand, and on the same note, do you have the papers that came with the rev control to insure that it is properly wired to the dist?
Also, how is your dist. locked out? Riveted or welded? It is possible that whoever did it may have gotten a metal shaving or slag in the magnetic pickup directly underneath.

Yes stp you are correct, what I am saying is I have had the pig tail and the pick up one time wired to the plug so the wires met green green purple purple, and had to reverse them. They came out of the box this way. Sorry for the confusion, sometimes I dont type what I am thinking!

If you set the timing at 32 degrees at 1500 rpm and it is a locked distributor....it should be 32 degrees at 3000, 4000, 5000, etc. It should not gain more timing as RPM increases.

timing always bounces around on my motors in the shop

my motors all sound bad or rough in the shop up to 3200 rpm especially

I use a chassis dyno to tune my motors and dont start them at home much if it all.

This is what I tested:

The new distributor with Rev box unplugged
Same with tach wire unplugged as well
Changed to DUI distributor no rev box
Tried it without tach wire
Tried it with tach and gauge lights unhooked from power, distributor hot wire only hooked up

All come with a lovely miss around 3000 rpms plus or minus 500 rpms. It is a miss that would not be raceable. It doesn't go away with increased rpm. I went to a bottom of a hill and on the way back up, I held the throttle steady and it felt like the motor would eventually die if I continued for awhile. Throttle was steady, but rpm was slowly decreasing because of the stumble/miss/hesitation. It didn't jerk around but felt as if it would run out of fuel if I continued.

The carb I have has the clear glass sight bowls and the manufacture suggested running the floats to where I could see a small bubble at the top of the glass. The back bowl is SLIGHTLY higher than the front and this carb is setup with 1to1 on the secondaries. It got dark and started raining, but here is what I was going to try next:

Lower rear float slightly
Different carb (only have a 2 barrel availabile)
New toggle switch ?
My carter fuel pump that doesn't require a regulator
Carb builder suggested a ground strap from motor to frame. I've done it in the past but I didn't have it on last year's car, so I went without it on this year's car.

Is there anything else that I should check or move to the top of my list to check tonight before the carb?

im guessing you checked fuel pressure at 3k if not and its dropping maybe the fuel filter is installed incorrect? said it was a new motor not sure if it was changed or if a whole new car. just an idea.

Thanks for the reply. New car to me. I did check the fuel filter before hooking up all the fuel lines.

if this wasnt a racecar id say you have a clogged cat or restricted exhaust.have you put a vac gauge on it .check vac at stumble.low or no vac, check for valves to tight,or restricted exhaust. after sitting all winter we found a nest in a muffler drove use nuts.just a thought..

Tried the 2 barrel. No miss anywhere through the RPM.

Took new carb completely apart, cleaned every hole I could see. Put it back together and I would call it raceable now. There is a pretty big stumble around 2500 to 3000, then it clears up and runs pretty clean the rest of the way on up to hitting the 6200 chip. The carb builder recommends 7.5 for the fuel pressure. I did a test at that and at 6.75. I want to say it was a little cleaner, but don't really know. Can anyone clarify where I should be running the float levels. I've ALWAYS ran mine to where it just trickles out or comes out with a slight nudge on the frame. With these glass sight bowls, I have them all the way up the glass until the very top I've left a bubble. I don't know why I didn't test it with both bowls lowered a bunch. oooops

we run our 2 barrel so it just trickles out and our 4 barrels so when you bump the chassis they "spill"