'70 LT1 hi RPM problem

[adam schorr]

The all-stock 11:1 LT1 will not rev past 5300 rpm. It pulls strong until the fun is supposed to begin, then quits revving, breaks up, and backfires.

The engine was rebuilt in 1989 (I have photos, notes on specs, balancing, cam, etc.) and has approximately 10-12,000(?) miles since.

Note, this no-rev problem did not happen when I first bought the car in April 2002 when it recieved a basic tune-up after aquiring it.

Last month, the valves were adjusted, a new cap and rotor installed, the carb was "rebuilt", and an NOS Stat Pole from TI Distributor and upgraded circuit board (from TI Specialty) was installed.

The carb rebuild was minor. I think the mechanic ordered some sort of basic kit of gaskets, rod, etc?

Please offer suggestions and thanks!

[Michael H.]

Re: '70 LT1 hi RPM problem

Adam,

I would begin with a new set of spark plugs. All high compression engines eat plugs rapidly, especially if driven mostly around town, and the problem that you describe is one of the most common. If that doesn't help, there are several more avenues of search for the problem but some get more complicated as you go. Plugs are easy and cheap for a starting point.

If the plugs appear fouled when you remove them, you may want to step up the heat range by no more than one number.

Michael

[Terry M.]

Re: '70 LT1 hi RPM problem

I would second Mike's spark plug diagnosis. It happened to my 1970 LT1.

[Dave S.]

Re: '70 LT1 hi RPM problem

Adam,
I had the same problem with my 70 LT-1 when I first acquired it. It ran like it had a governor and would peak at 4000 RPM. When I was preparing for my PV I had to address the problem. I went to rebuild the carb. and I found the primary fuel bowl full of schellac. All the years of non use caused the problem. I simply was not getting nearly enough gas to go over 4000 RPM. Were you able to solve your throttle shaft problem.????

[adam schorr]

Re: '70 LT1 hi RPM problem

Michael, Terry, and Dave,

Thanks for the suggestions. Dave's description, "It ran like it had a governor and would peak at 4000 RPM" is a great description...Only mine is peaking at 5300 RPM. Won't spin faster.

With regard to hotter plugs, I'm not sure what 'one step up' means, and, I don't know what plugs are in there.

Firstly, do I need to know what's in there in order to know what one step up looks like? Or, could someone recommend a specific type? Fouled plugs have black, caked-on carbon, right? If I'm running lean, they'd look white, right?

Dave, I purchased the Dry Graphite Lube from NAPA, and plan to carefully spray it in the throttle shaft area, and will let you know if I made a mess.

Thanks again!
Adam

[Dave S.]

Re: '70 LT1 hi RPM problem

Adam,

The original plug for a 70 LT-1 is an R43. An R43 is far to cold for nornal driving so I would suggest you use an R44 or R45. The last number is the heat range with 5 being hotter than 4 or 3. I personally like AC plugs but others who lean toward Champions or some other brand can give you the respective numbers. Change the plugs and check the primary fuel bowl for starters. It sounds like you definately have a gas problem and not an ignition problem.

[George J.]

Re: '70 LT1 hi RPM problem

Adam,

check with the mechanic that did the tune up and make sure he used a set of points that had a high tension spring. If he used some basic set that came with a "tune-up kit" they may not be strong enough. If that is the case, get a set of Echlin or Blue Streak.
George

[Joe C.]

You Have Points Bounce

Use points with high spring tension.

[William C.]

Re: You Have Points Bounce

Also check the "new" rotor in the distributor. Service replacements are shorter than the originals and do not work as well is a SHP engine. Try an accell rotor, in addition to the comments above.

[Terry M.]

Re: You Have Points Bounce

Joe & George,
If this 1970 LT1 is equipped as the factory assembled it -- it has no points. K66 Transistor Ignition was an included part of the 1970 and 1971 LT1 option.

[Robert E.]

Re: You Have Points Bounce

Joe,

Unless it has been replaced with pionts, all Lt-1's came equipped with TI.

Robert

[Drew P.]

Re: You Have Points Bounce

Hello Robert,
The 1972 LT-1 did not have the TI system. The 1970 & 1971 did have the TI system.
Regards,
Drew Papsun

[adam schorr]

Re: You Have Points Bounce

Wouldn't the installed NOS Stat Pole from TI Distributor and upgraded circuit board from TI Specialty mean there are NO points?

[Drew P.]

Re: You Have Points Bounce

Hello Adam,
Yes, your are correct.
Drew Papsun

[Joe C.]

Thanks. I Stand Corrected!

I should have read the initial post more carefully. My response is what you might call a "knee-jerk" reaction to earlier SHP hi-rev problems.

Joe