I got a freshly stock rebuilt 68 200 six with a two inch 1 to 2 carb adaptor running a 350 holley. Ignition is a 78 duraspark dist. (remain unit) with a msd tfi coil and a hei moduale. The 65 econo runs great, after I put a new muduale in it that wasn't fried, But can't get her to go over 4200 rpm, she stumbles hard and loads up a bit like I've lost my spark. Everything is new on the truck,wires,plugs, cap n rotor,ignition moduale, completly rebuilt carb. any thaughts? I've tried about everthing. oh timing is a 12 with 15 mechanical coming in by 2500 and about 40 total advance.
tops out at 4200
- Thread starter wtrmrk
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More Than Likely the Valves are Floating above 4200 , if they are the original ones , the motor should hit 5000 easy but why ? , nothing you have done to it warrants that rpm ,
Heck leave it there, you won't hurt anything.wtrmrk":2e5a0401 said:
I give mine a WOT run every now and then and with a modified head, stock carb, stock exhaust, and the 264/274/112 cam she creeps up over 4500. I'll need more carb to get any more out of it, but there is definitely more to be had.
Possible fuel starvation??
Does it happen only under load???
Take it over 4200 with no load & see if it still acts up. If it does hook up a timing light & see if the timing mark is steady or just goes spastic.
If it goes spastic its ignition.
If it is valve float you should hear noise from the valve cover area.
Check fuel pressure under load. Bill
Does it happen only under load???
Take it over 4200 with no load & see if it still acts up. If it does hook up a timing light & see if the timing mark is steady or just goes spastic.
If it goes spastic its ignition.
If it is valve float you should hear noise from the valve cover area.
Check fuel pressure under load. Bill
something sounds wrong IMHO, IIWIYS I would replace the duraspark dist with a reman form napa or a dealer if possible, then i would find some fatter jets for your carb, it just don't sound right from your description. (do one thing at a time for troubleshooting)
my 1bbl can rev up 5500 no problem, I can comforatbly accel up to 5200rpm, and my sig compared to your setup you should have your top end your missing.
Looking back at some of my dyno runs I have my completely stock engine run up to 4300 with my auto tranny... and only 4k with my t5 tranny (still stock engine) not only was this completely stock but I was also lean, I was running avg of 14.1 ratio, not very good.
I remember with the new engine I got some bigger jets and felt the difference in the top end (deffenitly seat of my pants feeling) and the fact that with the bigger jet I noticed WAY more rpm's, I able for the first time reach 5000rpm on my new engine, sadly I never got to test bigger jets on my stock engine.
so I agree with wsa111, it's either fuel or spark, start there.
my 1bbl can rev up 5500 no problem, I can comforatbly accel up to 5200rpm, and my sig compared to your setup you should have your top end your missing.
Looking back at some of my dyno runs I have my completely stock engine run up to 4300 with my auto tranny... and only 4k with my t5 tranny (still stock engine) not only was this completely stock but I was also lean, I was running avg of 14.1 ratio, not very good.
I remember with the new engine I got some bigger jets and felt the difference in the top end (deffenitly seat of my pants feeling) and the fact that with the bigger jet I noticed WAY more rpm's, I able for the first time reach 5000rpm on my new engine, sadly I never got to test bigger jets on my stock engine.
so I agree with wsa111, it's either fuel or spark, start there.
does it in neutral too, with the timing light hooked up the light begins to become spuractic a little too, old hei moduale was bad so just installed a new one. the dist. is a remain off of ebay, pulled plugs and I was running on the rich side of things(dry sooty build up) so dropped one jet size when I rebuilt the carb, plugs are now a nice tan color. have not checked fuel pressure yet but have a gauge that will be installed with my new electric pump and regulator. also what about the stator pickup in the dist. ? could this be giving me spuractic spark at higher rpm? Well try a few more things in the evenings but running out of ideas.
wtrmrk":376b7n4q said:
Heck, you have narrowed the problem to the ignition system.
You can ohm the pickup coil, i believe the range is 400-800 ohms. If you check it cold get a reading, then get a reading hot. You can always heat the coil up using a hairdryer. Good luck, Bill
ohmed out the pickup coil last night. It ohmed good at 650 but when tested ac voltage it would only put out .8 vac. So tested my spare out of another dist and it produces 1.5 vac changed it out and it runs bettter, now I'm getting steady spark all the way up on the timing light, no to address the to much total advance issue. I recurved the dist and mechanical advance comes all in by 2500 rpm at this point I'm running 10 degrees initial and about 15 mech, so I'm at 25 but with the vacuum hoocked up I get another 15 degrees bringing me to 40. should I just retard the initial a bit more? or is there a way to tweak the vacuum advanve? thanks
At WOT you shouldn't be getting any vacuum unless you're using a load-o-matic carb port. Timing should be initial + mechanical = approx 32-36 degrees. The vacuum is only there for part throttle, light-to-no load cruise conditions.
Set your initial timing with the vacuum unhooked.
Set your initial timing with the vacuum unhooked.
No that shows it is working 
okay I am pretty sure I have eliminated timing and ignition problems, but with the engine cover off being that it is right next to me in the cab I could diffenetly here the valve train rattle once I get over the 4000 rpm range. This is in a stock reman 200 so should I install a stiffer valve spring?
no I did not realize that there where two slots in the DSII for vac advance, but engines does with vac advance unhoocked too. and not only can I now here the valve noise (basically sitting on top of it with no dog house) it takes a few seconds for the engine to recover after a run up, so thats why I'm starting to lean toward valve float. So was thinking of trying a stiffer valve spring. This being said can I buy just any 289 valve spring from napa? or is there a perticulare one?
Did you check the lifter preload measurement it may be as simple as replacing the push rods for longer ones
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