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View Full Version : Zenith Carb - Jets for altitude



petru
08-23-2008, 10:35 PM
Running through everything that could be an issue in keeping my SII from running correctly. It came from 400 ft. it is now at 4500 Ft. Started doing the typical Zenith troubleshooting stuff so am working through all the tips here. Have it idling at 600 rpm pretty regular - BUT its still blowing some bluish/grey smoke. Figure I would be better off replacing these as well when I tear into the carb. Does anyone know the part numbers? I think I read somewhere there are two different sets? Up to 5000 and then over?

petru
08-26-2008, 08:58 PM
Nothing?

greenmeanie
08-27-2008, 12:27 AM
If its bluish gray smoke I'd be thinking oil. Rich running produces black smoke. If it only really does it on start up then I'd say worn valve seals. If it does it continually I'd say ringsor very badly worn valve guides. When was the engine last rebuilt and what's your oil consumption and compression like?

Cheers
Gregor

petru
08-27-2008, 08:15 PM
I haven't had it that long so have done one oil change and honestly haven't driven it probably more than 40-50 miles. I don't think it has really used any oil. I bought it from Oregon and frankly haven't checked compression yet but that sounds like smart advice.

Here is the story:
I drove it to work 13 miles one morning. On the afternoon drive home, 90+ degree day after driving about 6 miles, it was bucking and surging, it would idle but not move. After loading it on a trailer and getting it home tried running it again. Same problem - 80 odd degrees by this time. Figured a bad case of vapor lock.

A couple weekends later (Friday night) I drove it less than 5 miles - probably 3 - and after letting it sit for about 30 minutes started it up and drove it 100 yards - bucking, surging started again with no power for propulsion. Everyone there figured they knew the problem and started tinkering with mixture and idle (one was a guy that used to own a european car mechanic shop - he theorized the jets and fuel pump issue). I left it overnight - the next morning adjusted mixture screw until it would idle and drove home. Played with it on dwell meter etc. and have it to the point where it sits today. 600+ rpm idle and it blows the faintest blue smoke (most noticeable at start) and it ran well enough for me to drive it around neighborhood for ten minutes - but my reluctance to be stranded again, no trust from me and looming vacation means it will sit for the next two weekends - and until I gain trust again - it won't go far from home.

I am hoping to get some advice from you guys. It makes a lot of sense that honestly I think it suffers from a temperamental fuel pump (sometimes it seems to have good flow - sometimes) and too rich a mixture.

Ideas? I really doubt it has anything really major wrong with it as I bought it from a very reputable member of the forum.

ybt502r
08-27-2008, 09:33 PM
I possibly can help indirectly. I took a Series III from sea level (in the UK) to the mountians of Colorado (8000 ft). It had a Zenith, and it ran rich as a result. I still drove it around for a couple years before changing out the jet. I compromised to the one that's for 3000-5000 ft as the Rover is now in Calgary (3500 ft).

In reference to your problem, it never put out any bluish smoke, just the normal black tinged smoke that's the sign of running rich. (Gray smoke is oil, black smoke is fuel someone told me once.) Mileage wasn't that much worse, but mileage was never good to start. It ran a whole lot better when I finally got around to a full tune (rotor, plugs, condensor, etc.). In the drive to Canada, the Zenith apparently "warped" and it would run real rich with constant black smoke. That took a rebuild that eventually led to a new "rebuilt" Zenith, into which I've put the aforementioned 3000-5000 ft jet. It runs great now.

The high altitude jet could help, but your symptions as you relate sure don't point me to thinking that alone will solve your problems. Have you checked the other suspects - see the tune up bits above - and perhaps the fuel pump too?

petru
08-27-2008, 10:24 PM
Any chance you still have the jets from before your changing to the 3-5000 jet? Or where did you purchase your jet? I am looking for the 5000+ jet as I am at 4500 currently and plan excursions into the mountains so it won't take long to get higher - Salt Lake City.

I am thinking temperamental fuel pump (punctured diaphragm?) or just weak. I just drove it around the neighborhood (I love driving the dang thing) and not a puff of blue smoke. I am planning, upon return, to install electric fuel pump as one of my steps to getting this thing running good.

We pulled the line off after the fuel filter - the first time it had poor flow then the second time there was a noticeable higher flow - hence the temper-mental/weak pump idea.

All ideas are welcome. When I get back on 9/8 I want to really get this figured out. I am running out of quality top down weather!

greenmeanie
08-28-2008, 12:38 AM
Ok, Now we are gettign some better symptoms. I think there was a thread for Woodland 88 with similar issues that is worth reading.

Start from the carb back, splitting at each junction and checking the fuel flow. You've got each length of hose which at a very outside chance could have collapsed, I hope you have an inline fuel filter, then you have the screen at the

top of the sediment bowl adn finally you've got the most likely culprit which is the in tank pick up tube which can get blocked intermittently.

The mechanical fuel pump on my IIA wore out over many 10s of thousands of miles. It got weak but it did not produce stumbling. The symptom for that was that the egnien would rev to about 3600 rpm and fall flat on its face with no more power past that point.

As a reference I run a IIA in Phoenix and I've oinly had her vapour lock a couple of times after running hard for a bit, then stopping where she heat soaked and then trying to run again. That was on a 115+ day though. A bottle of water poured over the fuel line and carb fixes that in short order.

A little food for thought.

Cheers
Gregor

petru
08-29-2008, 08:57 PM
Green: Good to know. After it happening a couple times and in moderate temps I was a little suspicious that it might not be the issue. Keep the ideas coming. I need all the help I can. In florida right now and it is hard to believe but I am missing the ability to go work on that inanimate piece of recyclable aluminum.

ybt502r
09-02-2008, 05:00 PM
Petru, I still have the sea level jet that came with the Zenith - they are also available in the common rebuild kits that I've bought before, though I suppose the contents of said kits can vary. I bought the high altitude jet from Dunsfold when in the UK - though I've seen it for sale at some of the various LR parts dealers. Still don't think that the jet is necessarily your main problem.

Re the fuel pump and filter, that's still a line to check. I've had an in-line fuel filter that I keep taking out (it runs better without it), so I'm sure that I don't have the filter in the right spot. I had it up near the carb (easier to put in and check), but I've had a LR mechanic point out that it needs to be right next to the fuel pump to avoid the surging issues that I was experiencing. I've not replaced it, but it's something for you to perhaps plan ahead when you address yours.

petru
09-02-2008, 07:12 PM
Y - thanks for the continued input. I am going to start at the fuel tank and move forward until I get to the carb. I am planning to look into everything - even if in my exploring I seem to find the issue. I think I will be installing an electric pump. The carb is where I will start getting nervous. Feel confident on being able to handle everything else in a fairly straight forward manner but the carb will/does have me nervous. While I am at it I will be looking for why my gas gauge refuses to register. Nine short days before I get grease under my nails again! Undoubtedly I will need everyone's help as I work through this. Re/Learning how to work on vehicles is too much fun!