Stumbles and backfires at high revs

[im02crazy]

My 1966 WM300 ran like a champ in warmer weather, but wouldn't start without starting fluid recently in 30 degree temps.

Carb looked ok at first glance- gas squirts in when pedal depressed and I have an electric fuel pump and new filter inline at the carb (after market metal can).

Thinking I loaded up the engine with TOO much gas, I pulled the plugs.

The old plugs were gapped at 025-.028 but looked great (picture at http://www.flyingtigertransport.com in the News Section)

I changed the plugs with new R45 ones and gapped them to .035 to spec.

Started right up with the new plugs, but now misses above 3,000-3,500 rpm, loses power and backfires.

Could the gapping be the problem??

CARB UPDATE: In checking this out I also noticed that choke is NOT closing when the pedal is pushed down all the way (missing the linkage), nor manually because of binding in the carb throat (Carter Ball & Ball, E7T2). I will correct this.

Any ideas on what might be causing the break-up at high rev?
Thanks.

[Tom Petroff]

I would check the point gap(dwell)
By all means fix the choke.
It has to close completely.

Tom

[75Crew]

im02 - You might also want to check your distributor cab for a crack. Sounds like something that happened to me on a '59 Dodge 318 many years ago...

[im02crazy]

Thanks guys, both good thoughts. I really thought I had that carb nailed. Not sure where the accel to choke link got to. We probably have one in the yard or in the carb parts box.

I did a search and put a list together of maybe 30 results with same problem on small blocks - GMs, MOPARS, others, and a bunch reported back coil problems or fuel for this prob.

* I was running a resistor for this coil but jumped it out when hard starting. I'm wondering if the coil is overheating and faulting. When it warms a bit I will get that resistor back in the circuit.

Also, back to the carb, I forgot I had to do the seasonal change-over for the accel pump, I will also get that set when I fix the choke. Just to make sure, I'll pull the feed off the carb and run a fuel pump test (electric).

I'll report back what finally solves this.

[wayneh]

* I was running a resistor for this coil but jumped it out when hard starting. I'm wondering if the coil is overheating and faulting. When it warms a bit I will get that resistor back in the circuit.
.

Have you checked to see if the points are burned?

Wayne

[defdes]

Also, back to the carb, I forgot I had to do the seasonal change-over for the accel pump,

What's the seasonal change over?

[Gordon Maney]

There are alternative holes allowing accelerator pump linkage to be oriented so it either allows a longer stroke or a shorter stroke.

[im02crazy]

I forgot about this changeover. Other than this setting and my choke not working at all, I most likely didn't have a problem!

[im02crazy]

Findings

The basic problem was that my BB carb did not have a vacuum advance port. This mis-matched carb to 251 with vacuum advance distributor seemed to be part of the problem.

I replaced the carb with the model that originally came on the 66 and connected the vacuum advance. No more high speed stumble. BUT........

Just yesterday I experienced lurching and high speed lean-out/starvation. The fuel filter was almost totally clogged. Although my fuel gauge showed 1/2 tank it was nearly/totally out. I picked up lots of crap that clogged the fuel filter. I changed the filter and got home, but it's still a problem.

Next step: pull the gas tank, clean out (simple green/ or TSP) agitation with small jagged parts, rinse, repeat, heat dry, treat with ospho and re-install.

I will flush all lines, replace filters (first; in-line glass with super strong iridium magnets plastic-tied to the glass, second; big cannister filter), and will monitor the fuel at the glass filter. My have to replace all fuel lines.

[im02crazy]

Update: Pulled tank- got my exercise for the month

Pulled the tank and flushed. Got lots of rust powder out in the rinses. Not attracted to magnet cause they are fully rusted.

Power washed: Zep Purple washout, hot TSP soak and sheetrock nail agitation, more flushes (35), hair dryer force dry, muriatic acid (Lowes) 50% dilution for 4 hrs, then straight acid for 15 min at dip tube area where only rust in tank was evident.

Baking soda soak and agitation 30 mins; 1 hr of wash out; force dry.

Jasco rust proof (Lowes version of Ospho) for 1 hr - tumbled tank till fully coated. Force dry.

More to come of the re-installation tank mounting, line flush and carb flush + two new filters. Will calibrate the sender and the gauge to mke them match - and make it show nearly out when I still have at least 2 gals in the tank to help prevent sucking future crap/water.

Reminder to self: The tank has a drain unlike most modern wonders- drain the tank once a year !

Details on all this by Sunday nite June 23, on the flyingtigertransport.com site

[wayneh]

You may want to take your carb to Glen Burnie Carburetor. Bunch of good folks who know their shtuff and and check out your B+B/ They did mine and I'm happy. The one thing to think about that we don't really worry about any more is vacuum leaks. The PCV valve needs to be right. Jasper does not know anything about your vacuum system. When I got my truck home they had a manifold bolt that was too long so the carb never sealed correctly at the gasket... If you are really feeling non-motivated, drop your truck off at GB carb and tell them to make it run... They work on old cars and non FI cars.
And when you get bored bring her a bit further South to Davidsonville and we'll check it out. (we being me and my dog and my wife..., and maybe Doc Langford!)

Wayne

[KRB64]

A lot of work but it looks good!

In what section do you find the Jasco Rust Proof?

And what's that car in the back ground?

[im02crazy]

Jasco

Found the Jasco in the "cleaning" section (national layout is aisle 13). Strong stuff like ospho. I've used this approach for 5 or 6 tanks and it's holding up very well. I gave up on the inner coating process after testing the phosphotizing method. I routinely scope the tanks and they are doing well.

The Dodge's friend in the background is a 1970 BMW 2002 - also ospho'd tank back 7 years or so. Still fine. I've also noticed a cross over with Power Wagon owners with Airstreams (Fred Coldwell used to tow his with a Power Wagon as well; the caravans also used PWs as well as IH).

[im02crazy]

Carb service

Good idea Wayne. If this doesn't get it going I'll take the truck in to them. The Jasper rebuild was fine (minus the bad head gasket) but they don't run the engine on the carb- they use a computer to "simulate" ignition timing and mixture. It's taken me a while to eliminate all the gremlins.

I am regularly driving it now, and getting near the 500 mile first oi/filterl change. Hope to get it to a few shows!

[wayneh]

yea, I'm lucky my 230 seems to run well with the exception of oil leaks at the front and rear seals, and I've got too many projects to look at that quite yet. As you say, Jasper rebuilds the engine but does not test it... so if you have aair leaks, oil leaks, bad ignition timing etc it is not their issue. Regardless, while I'm not whizz, I may be able to help. And if not, we could at least have a cold drink while thinking about the problem!
Wayne