The Stovebolt Site Forums The Shop Area Engine Shop No power in 3rd... Chevy 261

Just completing a project and took it out for a quick test drive the last few days.. Very disappointing power in 3rd and 4th

The truck is a 1950 chevy 1 ton pickup with 1962 chevy 261. Rebuilt 261 specific rochester, good solid compression all around, timed with light to ball on flywheel ( believe flywheel is from 261.. Not earlier) .. Also tried timed by vacuum gauge, set carb with vacuum gauge, new glass bowl on top fuel pump, new lines. Adjusted valves when hot to .006 and .018.. Did it twice.. First time used ball on flywheel, second time used triangle

Truck starts great, idles great, has lots of get up in 1st and 2nd.. Will barely pull 3rd

The gas tank at present is a small tank zip tied to front spring with suction hose from fuel pump inserted to bottom of tank, checked with full tank.. Same power drop

Could the pump just be insufficent to lift fuel from approx 12 below pump and keep engine supplied in 3rd.. I think it shouldnt be the issue but thought id ask... New tank will be installed in about a week

Other suggestions.. With 5:14's i didnt think pulling 3rd would be an issue

It could be the muffler is plugged. Mice are very tricky.

No muffler at present.. Approx 2 ft straight pipe

Could the outlet on your substitute gas tank be to small or the vent in its cap?

John

guessing like everyone else here but maybe a bad spark advance is showing itself in 3rd/4th more than the lower gears. Does the distributor move when you gas it?

Rochester has a ported vacuum port hooked to vacuum advance.. The distributor moves (advances) as throttle is opened

Truck has good vacuum at idle .. Approx 21 inches and rock steady at 500-600 rpm

Are you sure you are getting full throttle?

The engine "works" less and less as you go up in gears so makes me think non "engine power" suggestions. 1st and 2nd would be the load gears and you have no problem? Also, if had never driven it before, maybe you are shifting into 3rd too soon. Bad clutch does not make sense, something slipping in trans? Good power in 1 and 2 seems to rule out engine. Not sure. What speed do you get up to in 2nd? What does engine sound like after shift to 3rd, revving higher than it's moving? shudder? bogging down? gradual speed build up?

rear gear too tall?

Hadnt thought to check if carb opened all the way.. Checked and yes it does. Engine just runs ratty as you put load on it in 3rd. It sounds more like it is having a hard time revving rather than something causing a big load and keeping it from revving. Dont think it would rev out completely under normal 3gear load.. Flat paved street.

Rear gear is 5:14... Shouldnt take much energy to roll truck down flat road at 25-30 with no load

Im leaning more towards fuel issues

I also switched to 12V. At present all i have wired is power through switch to coil. Foot starter. I went with an internal resitor coil.. No ballast resistor installed in power line to coil.. Any issues with this setup?

what rpm are you at with no power? maybe youre out of rear gear, like its rev'd about all it can. with a 3 speed your final gear is 1:1?

I would suggest using external coil with ballast if you have points.
I still can not see a motor operating well under load and bad when load is relieved. It seems like gearing/clutch/governor. I was thinking it was a 4 speed? You have still not stated the speeds you are obtaining in each gear. Whatever your final gear, 3rd or 4th (without overdrive)the engine/tranny ratio is 1:1 to the pinion. I know you are not doing this but is sounds like when someone shifts from 1st to 3rd or 2nd to 4th. Some others thoughts: valve float, points break down, shift linkage mixed up/tranny sliders or it's normal..... Let us know what you figure out.

Another guess, is coil wired properly? Negative side of coil to the points is correct. Reverse polarity produces a weak spark, engine will run fine unless under load. Have also seen a bad coil wire produce the same symptoms.

check the float level, its possibly set to low or not working properly. your running the float bowel nearly dry in first and second. with 5.14 gears that engine should pull right up to 40 to 50 mph in 3rd with no problem

Started a few tests this morning

1.. While ideling i removed spark plug wires from each plug one at a time and could not really hear any change in how motor ran.. Surprisingly ideled smother and steady even with one plug wire off???

2.. Put a nail in top of distributor cap coil inlet and then coil wire to nail.. When ideling i slowly moved coil wire away from nail.. Spark was yellow in color.. Very thin spark from wire to nail.. Spark would jump 3/4" or more

New internal resistor coil, points, condenser.. Which to swap out first?

Sounds like something in the fuel sys. a bad coil or a timing problem would show up thru out the gear range.When you shift into 3rd thats when the engine needs the most power and uses the most gas.Many times when there is a bad fuel filter it shows up first at speed say above 40 mph.Start by checking the filter if there is one than the carb,take it apart and clean it,fuel lines,go thru all of it,one thing at a time.


Pete

When removing a plug wire one at a time you should have a very noticeable difference. The engine should drop in speed and tend to shake a little.

Spark should be bright blue. Perhaps points aren't gapped right, or coil is not getting enough voltage. With an internal resistor coil you should have battery voltage at the + terminal of the coil.

Update

Have full battery voltage at + coil terminal, points were checked again and ok.

Took carb off and found vacuum hole to carb blocked with gasket. Fixed gasket issue and reinstalled.. Runs better in 3rd but still not correct.. Will go back through previous adjustments

Thanks for help and ideas

If it runs better for sure, then you are on the right track. Investigate all aspects of fuel/air delivery as mentioned, ALL fuel filters, tank pick up, pump, hoses, air cleaner/filter, PCV stuff, exhaust flapper stuck, octane and carb. I think you said no vacuum leaks?

Yes its definitely running better so on correct path

Took carb apart and found float level a bit high so adjusted it down. The accelerator pump is acting up also.. Very weak shot... Linkage is moving but pump not making full stroke... Will look into it tomorrow

Overall it is looking more like fuel problems.. I am going to switch a carb off a good running 235 this coming week and see how that work

Thanks again

Although a 235 carb will work it is a smaller CFM and will limit top end power.

UPDATE

replaced the 261 specific rochester with a rebuilt zenith from a gmc 270... truck runs much much better... pulls 3rd and 4th gear easily

also re-set timing to ball on flywheel, re-adjusted valve when at triangle on flywheel, adjusted carb by vacuum method, and added pertronics electronic ignition

overall starts, idles, and runs out very well.. based on the results from each change it looks like carb change made the biggest difference

thanks everyone for suggestions and help