MG Sports Cars

I have a 79 B with a 3.9L Rover V8 and Edelbrock 1404 500 cfm Carb. Starts very easily, runs very well (a little hot) and plugs are fouled, like it's running too rich. Owner's manual seems to have EXTREME amount of information on tuning this carb - is there a better source of info that makes tuning a little simpler?

Hey Don - I too have a 1404 on my 3.9. Starts easily, runs great, just drove 285 miles on close to a full tank of gas but, me thinks mine is runny rich too. I smell fuel all the time (no leaks) and a couple of non-professional mechanics (such as I) have also commented they think it's running rich. A quick search of the archives revealed that maybe a change in the rods and jets might be the ticket (may be that the stock rods and jets are a bit of an overkill for the 3.9?).

Here's what I suggest, gents. I've got the 1404 on my 3.5 and after much trial and error, I've come up with the following rods and jets.

Primaries; .080" (part number #1421)
Secondaries: .086" (#1423)
Rods: .062 x .052" (#1441)

I've chatted with RPI Engineering in the UK (Rover specialists) and this is the combination they use (except for the secondaries which I changed on my own to meet emissions testing here in Vancouver).

With any luck, this should work even better on your 3.9's. Trying to find a carb small enough for these engines is tough as the 3.5/3.9 only needs about 350-400 cfm to operate properly. I do like the Edelbrock for ease of maintanence and been able to change out rods and jets.

Any questions, ask away.

Cheers
Simon

I'll give this a try - thanks!

Simon,

Since I don't have to be concerned with emissions in my area, did RPI recommend different jets for secondary or just leave them as they are? Thanks for the info. Something else to add to the to-do list over the winter!

My wife and I did the loop out your way a number of years ago. Loved it - great scenery, great weather, great boating, great coffee and great beer!

Cheers, Tony

You're welcome, guys.

Tony, no changes to the secondaries from RPI. Just the primaries and rods. Wish I didn't have to think about emissions (well, at least as far as a car that only does 3000 miles a year!)

Keep us posted. I'll be interested to hear how you both make out.

Cheers
Simon

When I moved from North Carolina to Colorado, my car came under emissions testing... the requirement here is once-every-five-years for cars with "collector" license plates. (Not a bad compromise, I think.)

Anyway, my car failed the test on the first try... and frankly it wasn't running that great on the thin air anyway. (We're about 5000 ft above sea level.) I took it down the block to a local one-man shop and got his help rejetting the carb - we actually strapped his exhaust analyzer into the car for quick test drives (which was nuts... but worked out okay. I made a friend that day.)

This summer I welded O2 sensor bungs onto my exhaust system, but I haven't bought a wideband O2 sensor yet. With that nifty tool, I should be able to really dial in (or at least confirm) the jetting under load, and also better dial in the ignition advance curve. (Just in time to start installing EFI.) Don, if you can justify buying an O2 air/fuel gauge, I think that would be the way to go! Some of your symtoms don't sound quite right to me. If you're running rich now, then leaning up the mixture will tend to make your engine run even hotter. (Remember what they say: "Nothing cools like fuel." You might want to re-check your timing...) The gauge will at least remove any doubt.

Good point - thanks for the input Curtis.

OK, I assume I use the O2 air/fuel gauge in the exhaust (not a permanent sensor - or is it?). Does the gauge have instructions on what proper results/settings are? I've got a lot to learn in this area. When I put the Carb on, the car started on the first turn! After that, it's had so much power (compared to my "stock" MG), I didn't think about "tuning" (until I saw plugs). I know 1) it's the "green" thing to do; and 2) someday I'll want to do EFI.
Thanks for the help - Don Faber

Haha.... I know what you mean, Don. I wondered myself after the car had run a few times why I didn't need any choke.

If it helps out, I've got to get the car through emissions testing in the next while so I can post results if that helps anyone out.

Simon - Sounds like you're driving the same car I am! I never touch the choke.

donfaber Wrote:
-------------------------------------------------------
> Simon - Sounds like you're driving the same car I
> am! I never touch the choke.

Me too!

Simon: A follow-up post after your emissions test would be great.

Don: Came across this article regarding this A/R meter while researching 302 builds -
[www.fordmuscle.com] - there is a link to FAST's website or go
directly to www.fuelairspark.com.

Curtis: Are you familiar with this product? Looks good - although there may now be other products out there that
have comparable features and pricing.

I'll post the results as soon as it passes....."he says optimistically"!

The first link is a GRM discussion on a previous group buy for a WB O2 meter. The second is self explanatory.

[grassrootsmotorsports.com]


[www.14point7.com]

I've installed a A/F meter made by Wide Band Commander and it has worked well. It's really quite simple to install once the O2 bung is welded into the exhaust. It comes with a analog dash gauge that is a match to Auto Meter's Sport Comp gauges. It is also set-up to handle up to 10 minutes of on-board data storage that can be downloaded to a laptop. I was having a lot of trouble getting my Carter 9400 set to run right at our altitude here in Salt Lake City (4500MSL) and the A/F meter really helped to get it dialed in. It's also very helpful in letting me know what's going on if I get a misfire or stumble as the outside air temp changes or as I travel up or down in altitude. Jets and Rods are really a compromise situation when running in the mountains, and an A/F meter makes finding the right combination much, much easier.

Update on emissions: car passed with flying colours yesterday. Here's the stats:

Driving test (about 30 mph for a couple of minutes):
Hydrocarbons (ppm): 41.0 (max. allowed: 274)
Carbon dioxide (%): 0.26 (2.09)
Oxides of Nitrogen (ppm): 765.0 (2886)

Idle test:
HC: 176 (401)
CO: 4.32 (4.41) Bit close on that one. Closest it's being in 4 years. All other numbers well below the values allowed.

All I do to get the above readings is to increase the idle rpm to about 1100 rpm. No adjustments to mixtures.

OK - still have the 3.9L rover v8, 1404 Carb. Plugs really look good now (no sign of rich mixture), but they are almost 20 years old! What plug do "yall" recommend?

Probably NGK BP6ES. What comp. ratio, Don?

What is the jetting specs for your carb?

Carl - thanks for the plug info...

Been a while since I did the rods and jets - my notes show both primaries 0.080 (part #1421), secondaries 0.086 (part # 1423), rods .062 x .052 (part # 1441). Hope that makes sense!

Don

Carl,
Forgot to answer compression question - Engine was (is?) a new 3.9L short block supplied from the UK in 1998 - data I got showed 9.35:1 ratio (as I recall). My calcs at the time confirmed the ratio.

Don