2F engine running rough

Joined
Jun 19, 2021
Messages
11
Location
sacramento, ca
Fellow mudders, hoping to get some help. I’ve searched for results on this, but didn’t find anything that matched my situation.

Here’s my situation
2/75 Fj40 with 80k original miles (afaik)
Had been running ok, but recently developed a ‘miss’ that is worst at higher loads (climbing hills) and the idle has gotten rougher.

I checked/adjusted valves, nothing seemed too far off.

I went through the dizzy- check spark, new cap/rotor/wires/plugs. checked the mechanical advance, which seems slow to return - not sure if that is contributing to my issue?

Carb seems ok, a little on the rich side, but I would expect all plugs to foul equally if it was a carb issue.

Ran compression test numbers looked ok/good to me; cylinders 1-6 were 145,141,145,144,141,145. 2 and 5 were the lowest, but not crazy low.

Checked vacuum at brake booster. Vacuum looked good at 18, steady at idle with maybe a slight ‘tick’. Seemed inconclusive, other than to rule out intake manifold leaks, but I’m a newbie so ?

Put in new plugs, and plugs 2 and 5 fouled pretty quickly after a few mins at idle. Plugs 3 and 4 were dark, but not shiny with oil, and plugs 1 and 6 were perfectly clean.

Ran leak down test - somewhat arbitrarily chose 80psi as the pressure. Not sure if I should sneak up on it with the regulator on not?
#2 showed 66 psi and #5 showed 63 when 80psi was put on the cylinder, the rest we’re closer to 70. The majority of the leakage was coming out the head (it was loud out the bulkhead fitting where the head cover vent is routed to the carb) no noticeable leakage out the carb or the exhaust.

I’m thinking it’s valve guides/seals, but I’m hoping for a second opinion from the wealth of knowledge on this site.

Also, if I’m right, is it feasible to ‘just’ replace the valve seals with the head on, or should I take the head to a shop to have them go through it fully?

Any other ‘lower cost options? I’m running 10w/40 Dino oil, maybe go to 20w/50?

I’m running NGKBPR4EY plugs, maybe go a step hotter?

Thanks gents.


First pic is a brand new plug in #2 after a few mins of idle.
1645897645904.jpeg

Second is of #5 and my setup
1645897591934.jpeg
 

middlecalf

SILVER Star
Joined
Jul 20, 2004
Messages
4,522
Location
Sweet, Idaho
Any smoke out the exhaust, and if so, under what conditions and what color?
 

middlecalf

SILVER Star
Joined
Jul 20, 2004
Messages
4,522
Location
Sweet, Idaho
So I’d say the stumble is from the fuel end of things to include potential vacuum leak (idle vacuum looks great though). Do you have a manual choke, and if so have you tried chocking it a bit to see if the loaded stumble goes away (and idle smooths out albeit at higher rpm’s)?
 
Joined
Jun 19, 2021
Messages
11
Location
sacramento, ca
So I’d say the stumble is from the fuel end of things to include potential vacuum leak (idle vacuum looks great though). Do you have a manual choke, and if so have you tried chocking it a bit to see if the loaded stumble goes away (and idle smooths out albeit at higher rpm’s)?
PO put on a Weber with an electronic choke. I did try running it with the choke disconnected for a bit, but didn’t really notice a difference in how smooth it ran.

Not sure how I could mimic what you mentioned with my setup.
 

pjohnson

SILVER Star
Joined
Jan 15, 2003
Messages
2,892
Location
Idaho
Put an OEM Aisin carb back on it.
Contact Mark @65swb45 at Mark's Off Road or Jim C at TLC performance.

Or buy one off the classifieds and rebuild it with a kit from @cruiseroutfit Cruiser Outfitters.

Your Weber is crapping out and not a good match for the 2F.
 

middlecalf

SILVER Star
Joined
Jul 20, 2004
Messages
4,522
Location
Sweet, Idaho
I don’t know anything about Webers, and only a little about Aisins and various Carters. When a carb “craps out,” that’s usually from dirt or bad fuel, sometimes a float will have a catastrophic failure (leak) and fill with fuel and then the carb floods. I can’t speak to the mismatch issue between webers and 2F motors either. But the OP @Amplejohnson had a running rig that’s now started to stumble, so that’s a failure thing not a mismatch thing.

The reason I asked about the choke is, as a carb gets dirty, a lot of times the transition from one speed circuit to another becomes difficult and often the impact is immediate. Generally, there is an idle circuit, a low speed circuit and a high speed circuit. Transitioning between these is a function of air flow and fuel availability, both of which can be impacted negatively by dirt in the carb. A stumble from low speed to high speed might be lack of sufficient fuel - accelerator pump not squirting - or plugged orifices that prevent the high speed circuit fuel from being pulled into the carb venturi. Using some choke helps with this by reducing inlet fresh air - so fuel/air ratio is increased - and increasing the idle so that the transition to the high speed circuit is sort of bipassed (or rather “tricked”). If using the choke helps with the stumble then that’s an indicator that your low and/or high speed circuit is compromised (aka dirty). Of course, when most carbs are cleaned, all circuits are cleaned if done properly. So a carb cleaning might be in order.

Sorry for the long diatribe. A bit of a reaction to another “bad mismatch” argument for the cause of a “running ok” motor to not running ok.

I am a bit puzzled that that plug picture shows wet oil on it but you say there isn’t any exhaust smoke and you’ve check spark - at all plugs, right?
 

fjwagon

SILVER Star
Joined
Dec 7, 2004
Messages
1,955
Good work on the trouble shooting. At this point I would add a can of Seafoam. That stuff really works wonders. It may not fix your promblem but it never been done its good preventive maintenance. Another issue you may have is leak at the intake/ manifold and head area. I have removed them together and had them resurfaced at a machine shop and mechanic shop that has a table grinder. Other have used double gaskets to fix this same problem. Used water/soap spray bottle trick to see if you other leaks. Also run the engine check for arcing in the dark. If you see any arcing use silicon to insulate it. Make sure all your spark wires are seated correctly on both ends. Anyhow, good luck.
 
Joined
Jun 19, 2021
Messages
11
Location
sacramento, ca
I don’t know anything about Webers, and only a little about Aisins and various Carters. When a carb “craps out,” that’s usually from dirt or bad fuel, sometimes a float will have a catastrophic failure (leak) and fill with fuel and then the carb floods. I can’t speak to the mismatch issue between webers and 2F motors either. But the OP @Amplejohnson had a running rig that’s now started to stumble, so that’s a failure thing not a mismatch thing.

The reason I asked about the choke is, as a carb gets dirty, a lot of times the transition from one speed circuit to another becomes difficult and often the impact is immediate. Generally, there is an idle circuit, a low speed circuit and a high speed circuit. Transitioning between these is a function of air flow and fuel availability, both of which can be impacted negatively by dirt in the carb. A stumble from low speed to high speed might be lack of sufficient fuel - accelerator pump not squirting - or plugged orifices that prevent the high speed circuit fuel from being pulled into the carb venturi. Using some choke helps with this by reducing inlet fresh air - so fuel/air ratio is increased - and increasing the idle so that the transition to the high speed circuit is sort of bipassed (or rather “tricked”). If using the choke helps with the stumble then that’s an indicator that your low and/or high speed circuit is compromised (aka dirty). Of course, when most carbs are cleaned, all circuits are cleaned if done properly. So a carb cleaning might be in order.

Sorry for the long diatribe. A bit of a reaction to another “bad mismatch” argument for the cause of a “running ok” motor to not running ok.

I am a bit puzzled that that plug picture shows wet oil on it but you say there isn’t any exhaust smoke and you’ve check spark - at all plugs, right?
So, it looks like the new plugs I got were a step colder than the ones I had in before, so I think that contributed to the issue.

Also, I put a white bucket behind the exhaust and ran it for a bit. Did notice faint black smoke on acceleration, so I’m guessing that’s oil?

Also based on the guidance above, I took a look at the choke. It’s not electronic, it’s a thermal driven spring that closes the butterflies cold and opens them as it warms. Problem was, the unit was clocked such that it was always choked even when it warmed up, so the butterflies were always a little more closed than they should be.

It has always run a bit rich, so that seemed to be a contributing factor. I put the hotter plugs back in, and it’s running much better, still a little stumble under load, but not nearly what it was.
 
Joined
Jun 19, 2021
Messages
11
Location
sacramento, ca
Put an OEM Aisin carb back on it.
Contact Mark @65swb45 at Mark's Off Road or Jim C at TLC performance.

Or buy one off the classifieds and rebuild it with a kit from @cruiseroutfit Cruiser Outfitters.

Your Weber is crapping out and not a good match for the 2F.
Funny you should mention the Aisin carb. I got the original unit from the PO, and I’m working through a rebuild.
1645925446961.jpeg
 

TheHardWay

Ain't as easy as it looks
SILVER Star
Joined
Dec 29, 2013
Messages
1,723
Location
Las Cruces, NM
If you haven't already, check out Pinhead's Youtube videos. I've rebuilt two Aisans following them. Dude knows his stuff.
 

Users who are viewing this thread

Top Bottom