A Little Throttle Is A LOT Of Throttle

thrutraffic · May 25, 2020

1952 8N-B

Just did a carb rebuild. All seemed to go well and the engine starts/idles great. But if I increase the throttle lever position the engine goes immediately to high revs. There’s no incremental climb in revs. This occurs over two or three bumps under the throttle indicator sweep.

I’ve got the master jet out two turns and the idle jet out one. Moving the throttle doesn’t over accurate the linkages so I know it isn’t a mechanical action causing it.

I’m pretty sure the problem is that I didn’t do something correctly either new carb parts.

Anyone know right off what would cause this?

Jim L WA · May 25, 2020

Double check the linkage from the governor to the carburetor. If your sure that's correct, then remove the link from the carburetor throttle shaft and the governor, start the tractor and manually open the throttle by hand and see what happens. Let us know and we can go from there.

thrutraffic · May 26, 2020

Thanks. Will do today. I did investigate the governor linkage Because I need a new one. 😁 But it’s linkage functions seem to be working correctly; I.e. the stroke of the linkage isn’t enough to over-rev. I’ll check the throttle rotation and report back although I’m pretty sure just touching the throttle will instantly over-rev the engine. Stand-by.

wore out · May 26, 2020

Was the governor working properly BEFORE the carburetor work?

Did you remove the throttle plate?

Is it possible you mixed the control rods up at the governor?

thrutraffic · May 26, 2020

Took the govenor out of the picture.

Manually operated the throttle and idle goes to high rpms with a very slight throttle increase

wore out · May 26, 2020

"Took the governor out of the picture. Manually operated the throttle and idle goes to high rpms with a very slight throttle increase."

If you are manually operating the carburetor throttle butterfly lever/shaft it is NORMAL for the engine to race with just a little opening of the butterfly since it is not under load at the time.

(I would ASSUME you are not walking beside it and doing this while it is pulling a load???)

When it is "lugging" the governor has to open the throttle butterfly a considerable amount to hold a constant speed, but that's another matter!

thrutraffic · May 26, 2020

No. I have my creeper tied to the bottom so I can lay down as the tractor rolls along while I jerk on the throttle.

No way increasing the throttle a mm should cause that drastic a change in rpms. Driving it (from the seat) right now is crawl or run with only a one bump jump on the throttle lever. I’ve used this tractor for 15 years. This is the second carb rebuild.

Jim L WA · May 26, 2020

This what we were trying to prove. So it must be something you did wrong when you put the carburetor back together. I would suspect the throttle plate.

thrutraffic · Jun 2, 2020

Stumped.

FYI I replaced the govenor, not because of the throttle problem but because the housing was warped.

I pulled the carb, stripped it down while verifying everything was as it (I thought) it should be and put it back together again.

No difference in result; a little is a lot.

I checked the throttle assembly as suggested and cant find anything wrong there. I have the tapers in the correct orientation and the idle screw backed out to where it just actuates the butterfly valve plate. Manual actuation of the throttle or aviation by the throttle lever does the same thing; a little is a lot

R Geiger · Jun 2, 2020

To me it sounds like agovernor3 problem more than the carb.

soaked · Jun 2, 2020

Here are some test values from my great running 1950 8n, side mount, idle set at 400 rpm, no load, 2 arm original ford gov, m/s 241b carb, with pto turning.

Measured with small feeler gauge set, under the idle speed set screw.

.020 = 700 rpm
.039 = 950 rpm
.062 = 1250 rpm
.090 = 1700 rpm
.116 = 2100 rpm

I observerd when engine OFF, and quadrant 3 clicks up, there was .125 under the set screw---- more than enough to get high revs if gov not pulling back.( when running.)

3 clicks up on mine gives .020 and 700 rpm.

thrutraffic · Jun 2, 2020

Hard to believe a random new governor would exhibit the same problem. No?

For it to be the govenor Id get to see a long stroke of the throttle linkage with only a slight movement of the throttle lever on the dash, right. The throttle link from govenor to carb barely moves before I get high rpms.

thrutraffic · Jun 2, 2020

Ill try the same test. Have to use a timing tack since I dont have a proofmeter.

thrutraffic · Jun 3, 2020

Attempted measurement test. My timing light inductive pickup doesnt like the plug wires I guess so cant get accurate rpm readings to measure by. Skipping that as those arent directly relevant to this particular issue since a thousandth measurement here is probably a couple thousand rpms.

I swapped out the throttle shaft to the old one as theyre a little different. No effect. I disconnected the throttle to govenor linkage and actuated the throttle by hand and get the same result; a little is a lot.

Theres something about the rebuild and I cant figure it out; bad float setting wouldnt do this, it would either flood or starve. Venturi is in correctly. The jets appear ok but I have no way to measure them. Pretty sure the thread diffs prevent wrong jet wrong hole problems.

The only issue with the card is the eco mixer jet wont come out. If I twist any harder Im pretty sure the driver slot will strip. Best I can say is the jet looks shiny. LOL

Close to ordering a new carb.

thrutraffic · Jun 26, 2020

Just to cya; I also changed out the head gasket and installed a new manifold. Any chance something there could cause this problem?

HarryVanderpool · Jun 26, 2020

So, you installed an aftermarket governor?
BINGO!!!
And the bad news is that nobody on this forum has posted an explanation or fix (so far).
Read this:
https://forums.yesterdaystractors.com/viewtopic.php?t=1437605

soaked · Jul 2, 2020

Just an idea, is it possible the throttle plate is low at the rear, at idle? Is the idle set screw facing forward?
The screw should face to the rear, and the plate needs to be low in the front at idle. 😃

hunkydory · Jul 2, 2020

(quoted from post at 12:34:41 05/26/20) No. I have my creeper tied to the bottom so I can lay down as the tractor rolls along while I jerk on the throttle.

Sorry I can't help, but this was the funniest thing I've read in a while. Thanks for the laugh!

thrutraffic · Jul 22, 2020

Glad that made someones day! 😜

thrutraffic · Jul 22, 2020

(quoted from post at 11:01:53 07/02/20) Just an idea, is it possible the throttle plate is low at the rear, at idle? Is the idle set screw facing forward?
The screw should face to the rear, and the plate needs to be low in the front at idle. 😃

I dont think this is the case but Ive got another rebuild kit coming that has every new part possible in it. Well see. I verified the tapers on the existing carb were correctly oriented.

thrutraffic · Jul 22, 2020

(quoted from post at 15:31:51 06/26/20) So, you installed an aftermarket governor?
BINGO!!!
And the bad news is that nobody on this forum has posted an explanation or fix (so far).
Read this:
https://forums.yesterdaystractors.com/viewtopic.php?t=1437605

Was happening before I installed the new govenor. It also happens if I disconnect the govenor and operate the throttle manually.

wore out · Jul 22, 2020

(quoted from post at 08:44:05 07/22/20)

(quoted from post at 15:31:51 06/26/20) So, you installed an aftermarket governor?
BINGO!!!
And the bad news is that nobody on this forum has posted an explanation or fix (so far).
Read this:
https://forums.yesterdaystractors.com/viewtopic.php?t=1437605

Click to expand...

Was happening before I installed the new govenor. It also happens if I disconnect the govenor and operate the throttle manually.

"It also happens if I disconnect the govenor and operate the throttle manually."

Just trying to figure out what's going on here, and not knowing your level of experience with carbs and governors on old tractors, have you done similar things with other carbs and governors giving you familiarity with how these things normally work?

With no load on the engine it's NORMAL for it to over rev with the carb throttle butterfly opened just a little.

At low idle speed there's just a tiny gap between the throttle bore and the edges of the throttle butterfly, opening it just a small amount more will cause the engine to speed up greatly without a functioning governor connected to hold it back.

Only under a significant load can the butterfly be opened half or more without overspeeding the engine.

soaked · Jul 22, 2020

Glad you checked in. When I tested this carb before my last post here, I reversed the throttle plate. It idles fine---- then goes to high rpm as you describe. Thought for sure was your issue.

A Little Throttle Is A LOT Of Throttle

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