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Old 02-27-2019, 04:48 PM   #1
Dunedad
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Default 68 Scout 800, 152ci 4cyl, hesitates during acceleration

I have a 68 Scout 800 with a 152ci 4cyl engine. It has the original Holley 1904 single barrel carb, and a original Holley distributor that has been upgraded with a Pertronix Ignightor II pointless system. The fuel pump has been changed from mechanical to electric, and there appears to be a fuel pressure regulator installed inline to the carb.
The problem I'm having is when accelerating from idle at a moderate to fast rate, the engine hesitates/"stumbles" and backfires through the carburetor. This happens while at a standstill and while driving.
I have adjusted the air/fuel mixture screw to approx. 3 turns out from fully closed. The distributor set at 10 degrees. at idle and I've checked the best I can that the vacuum advance is functioning. Although I noticed that when advancing the throttle and checking the timing with a timing light, that when this hesitation happens the timing goes to the 0 mark.
I have checked the accelerator pump by looking down the carb and actuating the throttle, and seeing a good stream of fuel squirting into the carb, with the engine off.
If there's anyone that has suggestions on how to fix this problem please help.
Lyman Young
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Old 02-28-2019, 11:41 AM   #2
Greg R
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Even though the pump shots appear normal, the "timing" of the shot to the throttle plate change could be a tad off. Sometimes there's a bit of stiction on the plunger to the pump diaphragm. Facing the carb from the front fuel bowl side, the pump rod and cam are behind the fuel bowl on the left side. Put a squirt of light oil there on the rod the cam rides on.

Another thing is the pump link hole on the throttle, there are two. The inner one near the throttle shaft is the normal position. The outer one is for a stronger pump shot for very cold weather. If they get worn and sloppy, that can also affect pump shot timing or strength. Try the outer hole. I've included a picture.

If the problem persists, then it's an internal thing. Vacuum leaks on the body gasket, main well screws are loose, or dirt in the accelerator system not allowing the check balls to fully seat. These problems are corrected with a kit and cleaning in carburetor dip.

Three turns out for the idle mixture screw seems rich. If that is what it takes to idle normal, it could point to a slight vacuum leak affecting tip-in. Timing is set with the engine at idle, warm, and the vacuum line [U]disconnected[U] at the distributor and plugged when setting timing.
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Last edited by Greg R; 02-28-2019 at 11:47 AM..
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Old 02-28-2019, 04:17 PM   #3
Dunedad
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Greg, first off thanks for your reply.

Let me give you a little history about this Scout/carb. My father gave me the Scout a few years back. When he got it it had a Rochester carb on it and would barely run. This Holley 1904 was included with the Scout, and supposedly was the original carb from the vehicle. My dad rebuilt the card and was having the same problem when he gave my the Scout. I know that there are different rebuild kits, some better than others. The receipt I have for the rebuild kit says it was a "563" rebuild kit.

I've been doing some tinkering with the Scout and here's some more info.

In my adjusting the engine I found that by advancing the timing the hesitation (I should say that this is almost like a stall more than a hesitation, as the engine will actually die if I advance the throttle to quickly) seems to get somewhat better but not go away. I have the distributor advanced to almost 30 deg BTDC by using timing light. The problem with this is that as the advance is increased the idle is increasing, so much so that I have the idle adjust on the carb all the way out and it's idling at approx 1200 RPM.

I also adjusted the air correction screw inward to the point that the engine started to get rough, approx 1/2 turn from full closed and reversed back out approx 1/4 turn until it smoothed out. That is where I left it.

I also checked the vacuum at the port on the carb before adjusting today and it was at 10 in Hg just in case that might have been causing an issue with the vacuum advance.

I also want to mention that I'm at 4000' elevation where I live if you think this may be a factor.

I'm attaching some PIC's of my carb with the hope that we can identify what model carb I have and maybe this will help. I say this because the carb that you sent PIC's of differ some from mine. As you can see, my carb has 3 holes for the pump link, and the link rod doesn't have a cotter pin hole to adjust the link, so the cam has to be removed to adjust the link. Which hole should I use?
Also the air correction screw is in a different location.

Thanks again Lyman
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Old 03-01-2019, 04:24 PM   #4
Greg R
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Post EVERY number on the carburetor. Any number, except patent numbers, that you can find on the fuel inlet boss, the top of the fuel bowl, model number, LIST number or numbers.

From the pictures it does not look like a Holley 1904. Perhaps some over all view pictures of the carburetor body instead of close ups will help too.
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Old 03-01-2019, 08:13 PM   #5
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

You really don't want to be running that much advance timing as your initial, static setting. That is just a bandaid...and a very porous and virus infected one at that. You should be down around 10 degrees or less of static advance.
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Old 03-02-2019, 07:43 AM   #6
Dunedad
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Thumbs up Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

After further investigation I have discovered that this is in fact a Holley 1920 carburetor. Therefore I have ordered a new generic 1904 thru IH parts and will install it. Hopefully this will resolve most of my problems.

Thanks everyone for your advice and I'm sure that I will be posting on these forms as my adventure the Scout continue!
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Old 03-02-2019, 11:39 AM   #7
Greg R
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Quote:
Holley 1920 carburetor
That was my suspicion, but a picture would've confirmed it. Good luck on another carburetor. Scoutboy's advice is good. Go for original tuneup, ignition, timing, and carburetor specs.
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Old 03-02-2019, 12:54 PM   #8
Dunedad
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Well guy's I feel like quite an idiot.....
After further research I have determined that I have miss identified the engine in the scout. It turns out that this is a 4-196e engine. What a bone head mistake!
So now I will return the new carb ordered, unfortunately I don't see that there's a universal replacement carb for the 1920 available.
And now I will have to figure our what is going on with this carb still causing this hesitation.
Any thoughts would be greatly appreciated.
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Old 03-02-2019, 08:57 PM   #9
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Don't beat yourself up. That's been done many times before.
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Old 03-03-2019, 08:05 AM   #10
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

The best way to check the vacuum advance is with one of those small hand vacuum pumps that have vacuum gauges on them. I would also make sure the mechanical advance is working smoothly by disconnecting the vacuum advance and watching the timing while revving the engine a little.
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Old 03-03-2019, 08:21 AM   #11
Dunedad
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Thanks for the moral support Scoutboy...

I've gone back thru the distributor, cleaned and checked the advance mechanism to see that it functions correctly. Reset the timing to 10 deg.with the light. All seems to be functioning correctly, advance is smooth and linear.

I'm still experiencing the stalling/backfire and that makes me tend to believe that it's carburetion.

I've been searching the web to find out what I can about the 1920.
It seems like a good carb, very similar to the 1904.
The biggest problem I can see with it is the float. It seems that it's made of a synthetic foam called "Nitrophyl" and it can become saturated. That makes it not float/function correctly.
I'm wondering if the float on my carb is saturated and causing a flooding condition leading to this problem that I'm having??? I watched a video that showed that you can weigh the float to determine if the float is saturated or not. That's what I'm going to try today.
There doesnt seem to be any replacement floats available in the free world. and I'm not sure if there's and way to "dry" the float out.

I've posted about the engine seeming like it's not coming up to temp as well, I'm wondering if this might be contributing to this problem?

Well wish me luck as the adventure continues.....

Last edited by Dunedad; 03-03-2019 at 08:35 AM..
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Old 03-03-2019, 08:35 AM   #12
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

This isn't set in stone, but generally speaking, backfires that occur at the carb are the result of a lean condition. In other words, not enough fuel and too much air. Another way to describe hesitation is lean stumble. So, sure check your float. That's fine, but I don't think that's causing your problem. The thing is falling flat on its face when you shake the reins and dig in the spurs from a lack of fuel at that moment, not an excess.
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Old 03-03-2019, 12:23 PM   #13
Dunedad
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

FIXTIT.......

It seems that the diaphragm for the power valve had a fold in it thus causing a vacuum leak. Which was causing excess fuel to fatten up the carb.
After correcting this and readjusting everything to spec it's running like a sweet little sewing machine with no stumble or hesitation!!!

"When all else fails.... follow directions"

Thanks for your help!

So it appears that I have a 160 deg thermostat, I will change that to the correct 180 deg soon.
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Old 03-03-2019, 12:27 PM   #14
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Nice work! You're getting there.
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Lemuel - '73 1210 Reg Cab 4x4 CS - 304/TF727/NP205/4.09 FA25 & 4.10 RA16/6800# GVW - "Pull Lemuel, pull!"
Organ Donor - '72 1210 Reg Cab 2WD - seized 392/TF727/7500# GVW - "Use my body to keep you alive!"
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Old 04-07-2019, 11:13 AM   #15
samuel.cline.23@gmail.com
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Default Re: 68 Scout 800, 152ci 4cyl, hesitates during acceleration

Hey guys, I'm new to the forum. I have a 1965 Scout 80 152ci 4 cyl 4X4 Carburetor (Weber 32/36 I think) and a mechanical fuel pump. The fuel pump failed and I replaced it. Now I can't figure out what's wrong. Maybe I hooked it up wrong or maybe it wasn't the fuel pump to begin with. Can anyone confirm that I have it hooked up correctly? Thank you for your time.
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