Heat riser clogged?

[highroller]

Pretty sure I know the answer to this. Have 1600dp w/ 34pict3, and stock exhaust. Doing some other maintenance on engine (it's out of car) and suspected that a very slight stutter at easy throttle when engine below 160+/- deg. might be due to a blocked heat riser. So removed muffler and tried to blow compressed air (110 psi) thru riser , left to right. No can do, it doesn't come out other side. It's blocked right? It's supposed to be open all the way, right? Not gonna try to clean it out, or find a used one, just go new and be done with it.

[grandpa pete]

put a broken spedo cable on a drill and use that .
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63 two fold rag
66 sedan delivery Type 6

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[EverettB]

Yes, it should be clear.

If you can find a new one - Ok.

A lot of people have used a clutch cable to clean it out.
Put the cable in a drill and go to town.
Put the drill in REVERSE so it doesn't unwind.
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[wcfvw69]

I go to Home Depot or Lowes and buy some lengths of cable they sell by the foot. I had two different size. One shorter one to get it started and then a longer one for once I made some progress.

I also cut the end of the cable into a V to help it dig in. As Everett stated, run the drill backwards.
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[bluebus86]

what I have run into on several manifolds is the clog is so bad and rust so bad that the cable trick results in the cable punching thru the walls of the pipe! specially at the bends where the cable will rub the most. the clogs I ran into were rock hard, tough stuff, and the inside of the pipes were heavy pitted.

I have had some success with a high pressure bead blaster. stick that sucker right into the pipe and let her rip, it may or may not work, it is a sure fire way to blast out a rusty inside of an intake manifold however, the heat riser pipe could be too clogged and may resist all attempts at repair, (besure to clean out the grit really well!)

I have found that in a warm climate the heat rise function was not very noticeable. I have removed blocked ones off cars that ran fine, finding not much difference with a clean one installed, however I think in a cold climate they are really needed to be working.
Note that many gasket sets give two identical gaskets for the pipes to muffler This is wrong, at least on some models as one side (the one that goes right on top of the muffler flange, not the piped side) gets a gasket with a small hole. this helps maintain a pressure drop across the pipe and thus a flow of gas in the correct volume. so get the right gasket that has the tiny hole for best results. and put it on the correct side. if you cant find one, you can cut some thin stainless sheet and make one.

on one car with a hard to replace manifold I wanted to keep a number matching motor correct) I blocked off the heat risers on purpose to save the paper thin walls of the pipe that had internal corrosion, the exhaust c\gasses cause corrosion inside the pipes, and this one was pretty far gone, but still looked good, the car runs fine with it block, but again it is a mild climate for me and this car is somewhat a show piece car.
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[highroller]

Have some old cables, and will try that. Not for very long though. If it's real bad going to go with new.

['64cal lookdub]

Clutch cable worked good for me, I sprayed some brake clean inside as well. Some easy taps to the heat risers for vibration helps loosen up the carbon too.

[diablosandwich]

I have had some the cable worked after a while and some that were too tough for the cable. I took a 6 inch long 1/8" bit and made a pilot hole on the front side (it cannot be seen when engine is in car) then take a 12 inch 1/4" bit and drill out the carbon. The 12 inch long bit will not make it all the way but the cable then can finish the job. Weld up the hole and you are good to go.
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[wcfvw69]

While some bugs can run "ok" with the heat risers clogged, you'll notice an improvement in cold engine drivability with them clear. The same applies to having the fan shroud thermostat flaps and the thermostat hooked up.

I'm in Phoenix where it can get in the 30's in the mornings during the winter. The "drivability" improvement was amazing after I cleaned out the clogged heat riser and installed the flaps and the thermostat on a then new to me, stock 67 bug. You can hit the key, it fires right up and then immediately drive down the street.

My 70 bus I got a year ago needs the thermostat and flaps installed as they were missing when I got it. It takes 3-5 minutes to warm up before it's drivability is similar. I have the parts now and am going to reinstall them on it as well.
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[Cusser]

I'm also in Phoenix, and have a single Weber 40DCNF on my 1835 engine; its manifold has NO heat risers, never had any when new (back then I even had to make my own block off plates). I also notice that without these, even in Phoenix, that my engine stumbles the first few minutes in the cold weather (like a flat spot on acceleration, not on cruising), and no such symptom in out 9-month summers.

I'm also postulating that my non-thermostatted external oil cooler could also be a factor in that slower warmup/stumble.

I've just accepted that quirk with that setup, been 39 years now, so don't think that's going away any time soon....
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[yttkuar]

My wife and I were less than 100 yards from the entrance to our favorite campground, when our 71 Weekender quit. We were on the last slight uphill, not quite to the crest, when she took her last cough. A kind young guy jumped out and we pushed her over the knob and my wife coasted her in to the campground. I had completed the spring once over and up until that moment, the bus had been fine. Thanks to our AAA membership, we were towed home. ( 6 miles) If you do not have AAA, you should think about it strongly. We have 4 VW's and all but the 71 Ghia has take a ride. OK Here is what happened. The next morning I went out to push her into the garage to fix the problem. I tried to start her and she popped right off. I had thought it might be the fuel pump the day before, but it wasn't. So before throwing parts at it, I went in and consulted TheSamba. My first search was about stalls. Several things stood out and one caught my eye about vapor lock. I had started the bus several times and let it run for a little, enough to recreate the problem, I thought. With the lid up I noticed condensation on the intake just below the carb. TheSamba post mentioned the heat riser tubes being possibly blocked. We have had the bus for 6 years and I had never cleaned the carbon out, even though I had the engine out before. Who knows if it had ever been cleaned. I now will be checking all the vehicles for this potential problem. I blew air in. THEY WERE totally blocked. So here is what I went through to unblock them with the engine still in. I took off the bumper and muffler to get access to the riser ports. Some in TheSamba mentioned that it took them about 20 minutes to an hour to ream them out. NOT MINE! I spent 6 hours the first day and about 5 the second day, working the 3/16 braided cable back and forth. I used several lengths, each one a little longer than the previous. I cut the cables with my dremel square so that each part of the cable could dig into the hard carbon buildup. You have to run the drill in reverse so that the cable does not unwind. Don't give up! I thought about all kinds of alternatives, but nothing worked better than the cables. Finally, about 5 hours into the second day, and almost at the end of my patience, it broke through. I was a mess. Carbon dust all over my face and arms, my pants covered beyond cleaning...but through. So then, reinvigorated, I flared the end of the longer cables and reamed that son-of-a-gun out! After putting it all back together and starting it, I felt the riser tubes. The left one (drivers side) was hot, the right one was only warm. That was good. My muffler is a aftermarket as is my 73 Super and 74 Bug. The Ghia was hot on the right, warm on the left. So it is original I think. Anyway, all is good again.

[APPLEGREENVW]

Dual port heads intake manifold are available new.

https://www.cbperformance.com/product-p/3151.htm
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02/76 Beetle sedan

[difrangia]

[APPLEGREENVW]

Is that a CB performance or Empi manifold? If its a CB manifold did you contact them?
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02/76 Beetle sedan

[difrangia]

[APPLEGREENVW]