I have a 1975 Fiat X1/9 with a Weber 34 DMTR which was recently installed. After initial installation car ran GREAT! After about a week the car started running a bit rough, it would accelerate like it had a miss and would die when coming down of RPM. I removed it and cleaned out the jets and bowls. Upon reinstallation of the carb the acceleration went back to normal, however the idle still would not function when coming down from RPM. When the engine would die, upon restart it would idle but after accleration die again. I removed the carb and cleaned out the jets, pathways and bowls again. Upon reinstallation again now it won't idle at all below 1500 rpm but accelerates flawlessly. Can anyone tell me why this is happpening, and how to fix it please?
Weber 34 DMTR problems
- Thread starter Zauben
- Start date
Hmm..
While I'm not intimately familiar with the DMTR, I can offer some basic carb advice.
Have you tried adjusting the idle speed and mixture? Carbs come preset but you have to dial them in. Check for a vacuum leak as well.
While I'm not intimately familiar with the DMTR, I can offer some basic carb advice.
Have you tried adjusting the idle speed and mixture? Carbs come preset but you have to dial them in. Check for a vacuum leak as well.
Carb pics and layout
I was able to find a pic on google from TED with the layout of the 34 DMTR, and I have removed the jets and needles from the center as well as the venturi jets from the barrels cleaned and reinserted. I notice that the main venturi instead of spraying while at idle when I can keep it running "drips" into the barrel but as soon as you apply the gas it runs up the rpms beautifully. It had been suggested that I might have the wrong jets, however my misunderstanding then is why would it have run so beautifully upon initial installation?
I was able to find a pic on google from TED with the layout of the 34 DMTR, and I have removed the jets and needles from the center as well as the venturi jets from the barrels cleaned and reinserted. I notice that the main venturi instead of spraying while at idle when I can keep it running "drips" into the barrel but as soon as you apply the gas it runs up the rpms beautifully. It had been suggested that I might have the wrong jets, however my misunderstanding then is why would it have run so beautifully upon initial installation?
Ricardo Borja
el moco
your car has a pollution valves...
like air-pump, egr valve, gulp valve etc...
or your distribuitor vacumm has a little plastic valve between distribuitor and carb?
like air-pump, egr valve, gulp valve etc...
or your distribuitor vacumm has a little plastic valve between distribuitor and carb?
Dripping main venturi is one of the following:
- Float level is wrong (by far the most common problem)
- Crud in the needle valve, or worn needle valve (next most likely)
- Float is leaking or has sunk
- Gasket between the top and bottom half of the carb is damaged and not sealing, or the carb base itself is warped so the gasket cannot seal.
All easy to fix once the diagnosis has been made.
I know you're sick of cleaning it by now, but this cycle of removing, cleaning, reinstalling and seeing a different bad thing happen is still classic crud-in-the-carb disease.
- If you haven't replaced your fuel lines, do so. Old lines can look fine on the outside and still be shedding crud from the inside.
- replace the fuel filter.
- Fill the tank with fresh gas, use a bottle of fuel system cleaner, and don't let the tank get below half full for a while (fuel sloshes in the tank and can stir up crud from the bottom of the tank).
- In extremis, siphon the tank dry through the opening for the fuel level sender, taping the mouth of the siphon to a metal rod or something so that you can be sure that you're getting the crud out of the bottom of the tank. This probably won't be necessary, but it may be the only way of getting 36 years worth of crud and water out of there.
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I'm away from my diagrams now, but I can try describing it. The idle mixture screw is different for the 32 and 34 carbs, and there are two different styles of idle speed adjust.
Idle mixture:
On the 32 series carbs, it is a screw that projects from the base of the carb, at the back, head end pointing straight out to the rear. On some US-spec models it may be covered with a metal plug to prevent tampering. If the carb is off the car, you can look at the inside of the primary barrel and see the opening through with the idle mixture enters, and it's lined up exactly with the screw.
On the 34 series carbs, it is a little recessed screw in the base, on the left hand side of the carb (standing behind the car facing forward) and almost all the way back to the left rear corner of the carb.
Idle speed:
Two styles of setting, early and later. The later style is way more common on the 32 series.
Later style: There's a screw halfway up the backside of the carb, kinda over to the right of the centerline, head end points straight out to the back. This screw bears directly on a finger on thethrottle linkage, and it's easy to see how it holds the primary throttle butterfly just barely open at idle. You increase the idle speed by turning the screw in, further opening the primary. The directions posted at Peirce Manifolds and other carb vendors on how to set your idle speed and mixture are written for this style of carb.
Early style: The same screw is still there in the same place, but it is fitted with a lock nut and not meant to be adjusted - it just stops the throttle butterfly from closing so far that it would bind in the barrel. The idle speed is adjusted by turning a third screw, also on the backside of the carb about halfway up, but on the centerline. This screw opens or closes an air passage that goes around the throttle, so passes air even when the throttle is fully closed.
34 DATR thread in the archives
This looks like a long read, but might have a few nuggets Mike:
http://www.network54.com/Forum/12159/message/1151954169/34+DATR,+34DMTR,+and+jetting+(school's+in)
This looks like a long read, but might have a few nuggets Mike:
http://www.network54.com/Forum/12159/message/1151954169/34+DATR,+34DMTR,+and+jetting+(school's+in)
Erich did you get my pm a few days ago? I could really use suggestions. Pierce manifolds says they are swamped and it might be a while before they can help meI need my car driving ASAP as its a main form of transport, not a fun toy only. Thanks
I did see it... Sorry, I've been busy overthinking the answer. So I'll try underthinking: I actually have no idea what's right for a 34-series carb on a 1300 motor (I've done a 1500). However, I have found that if you take a 32 jetted for a reasonably stock 1300 and install it on a 1500, it is at least drivable, and a good enough starting point for more precise tuning. So I'll hazard a guess that you could go with the stock 34 jettings (if you can't find those .47 idles go for .50) for a 1500 and be drivable on your 1300.
I'd expect that no one is going to be able to come up with a spot-on jetting recommendation up front. You'll probably have to try something close and move a size or two up or down based on what you learn driving the car.
Eastep
True Classic
Jim: Thanks I have read that thread previously. Ive read literally every thread on the 34 series in the archives. Took me all day one day but I did it
Erich: Thanks also. I know that an exact jetting solution is too much to ask for, I'm just looking for a solid base to start at. It seems everyone uses the 34 on 1500 and so I assume that those suggestions would still run a little too rich and is most likely why I'm having an issue in the first place. Finding .47's is no problem as I'll just order them from Pierce. Would you (or anyone reading) recommend the jetting suggestions in the link Jim provided or use the jetting for a stock 32?
Could someone please post the correct Idle-Corrector-Emulsion-Main sizes for the 32 please?
PS: Sorry to thread jack, but its sorta killing 2 birds with one stone here.
Erich: Thanks also. I know that an exact jetting solution is too much to ask for, I'm just looking for a solid base to start at. It seems everyone uses the 34 on 1500 and so I assume that those suggestions would still run a little too rich and is most likely why I'm having an issue in the first place. Finding .47's is no problem as I'll just order them from Pierce. Would you (or anyone reading) recommend the jetting suggestions in the link Jim provided or use the jetting for a stock 32?
Could someone please post the correct Idle-Corrector-Emulsion-Main sizes for the 32 please?
PS: Sorry to thread jack, but its sorta killing 2 birds with one stone here.
dcioccarelli
Dominic Cioccarelli
Check the anti run on solenoid.
This will prevent it from idling properly if broken. To test, simply remove the rod from the centre of the solenoid and see if the problem goes away. Also, you should hear a "click"when power is applied.
Cheers,
Dom.
This will prevent it from idling properly if broken. To test, simply remove the rod from the centre of the solenoid and see if the problem goes away. Also, you should hear a "click"when power is applied.
Cheers,
Dom.
Jeff Stich
True Classic
Re: 32DMTR jetting
Page 52 of my Haynes Fiat X1/9 workshop manual says stock jetting for a USA 1300 with 32DMTR is:
Main: 1.10 primary/1.10 secondary
Air: 2.00 primary/1.95 secondary
Emulsion: F30 primary/F30 secondary
Idle: .45 primary/.60 secondary
My Haynes Fiat 128 manual says stock jetting for a USA 1300 with 32DMTRA is:
Main: 1.10 primary/1.10 secondary
Air: 1.90 primary/1.95 secondary
Emulsion: F30 primary/F30 secondary
Idle: .50 primary/.60 secondary
32DATRA is the same as 32DMTRA except:
Main: 1.10 primary/1.05 secondary
**Keep in mind this jetting is for USA 1300's with all the emissions equipment intact/operating. :fart:
Page 52 of my Haynes Fiat X1/9 workshop manual says stock jetting for a USA 1300 with 32DMTR is:
Main: 1.10 primary/1.10 secondary
Air: 2.00 primary/1.95 secondary
Emulsion: F30 primary/F30 secondary
Idle: .45 primary/.60 secondary
My Haynes Fiat 128 manual says stock jetting for a USA 1300 with 32DMTRA is:
Main: 1.10 primary/1.10 secondary
Air: 1.90 primary/1.95 secondary
Emulsion: F30 primary/F30 secondary
Idle: .50 primary/.60 secondary
32DATRA is the same as 32DMTRA except:
Main: 1.10 primary/1.05 secondary
**Keep in mind this jetting is for USA 1300's with all the emissions equipment intact/operating. :fart:
pyrraxis
True Classic
Every one that has posted has hit on some great stuff, but I think one thing has been missing - seriously cleaning out the emulsion tubes. It sounds like you still need to get the carb fully cleaned. This means taking the carb out, "boiling" it in carb cleaner (check out Tony's posts on this in the archives!) and making sure the jets/idlers/emulsion tube are completely clean. If you look at my recent posts I look like an FI guy, but my first X was a '78 and I learned everything I could about Weber carbs back then. Tore down and rebuilt more than a few in that time and one of the things that would consternate X owners is crud getting into the carb. EricH is dead on about what you need to check, but for the short term, pull the emulsion tubes and check them out. Even if they look clean, spray some carb cleaner into them (Gunk was the thing back in the day) and then clean them out again! I've actually found a pine needle in one of mine that did the same thing you're describing. It would run great at first, then it would crap out, then run fine again, then crap out - pretty much at random. Got that pine neeedle out of there and it was fine! I would still recommend renewing the feul lines and boiling out the carb, though...
Thanks for all the suggestions!
Hey Guys,
Thanks for all the helpful posts this week and suggestions. I have not had a chance to get around to looking at this yet but I hope in the next two weeks to get another shot at checking this out. Once I do I will report back my findings. I appreciate all the helpful advice and look forward to having this running again. Until then enjoy the holiday break, stay safe and burn the rubber.
Mike
Hey Guys,
Thanks for all the helpful posts this week and suggestions. I have not had a chance to get around to looking at this yet but I hope in the next two weeks to get another shot at checking this out. Once I do I will report back my findings. I appreciate all the helpful advice and look forward to having this running again. Until then enjoy the holiday break, stay safe and burn the rubber.
Mike