Can't hold 70mph

[Bent77]

Yeah that’s how I always did it. But I also knew where the advance was on the dizzy.

I’d probably check it, in plug the vac and check it, the set the base accordingly

The carb is probably set for sea level, but let’s make sure the timing and ignition are correct first. Also post your vacuum reading

 

[6.2Blazer]

I have a '90 K5 with the 6.2 diesel, which everybody loves to talk trash about how underpowered it is. With 4.10 gears and an automatic it would easily maintain 70 mph with a 4" lift, 37" bias TSL tires on steel rims, 1-tons, etc.... Granted this was at a lower elevation but point being you should be able to hold 70 mph.

4.10 gears on 37" tires and no overdrive in the transmission is not a bad gearing setup for running 70 mph on the highway at all. Not the greatest for acceleration from a stop but would give a good cruising RPM.

 

[Chevman88]

Just wanted to post back after today's...adventures...also, thanks for all the advice.

Once I got the truck warmed up and idle set to about 850, I found that base timing (no advance) was actually closer to 20, so I set that to 14 deg at 850 RPM which gave me about 23 deg with the advance plugged back in.

I think whoever put the edelbrock carb in used the idle mixture screw to set the idle as they were way off and the idle screw was just about completely backed out. I was only able to get about 15-16 in/mercury, but it ran much smoother after all this was adjusted and I was able to take her out for a test drive, much much better.

I'm sure there's a little more performance I can get out of it, but it really just isn't worth it to me at this point. She drives nice enough to last until the end of the summer where I'll start on the LS swap. At this point I'm starting to lean towards a built 5.3 and sticking with the TH400 for budget reasons. 6.0s out here are pricey...

 

[Blue85]

So reducing timing and adjusting idle mixture makes it hold highway speed better?.

What shape are the mechanical advance weights and springs in? Are they the stock ones? The midrange torque really wakes up when you let that timing come in faster. If you're heavy on the pedal on the highway, that vacuum advance isn't doing much. Your timing will come from the mechanical advance. I'm not suggesting you put much into it, but if you find something not right in the dizzy, linkages, choke, etc. you can get like 50hp for a couple hours work.

 

[Chevman88]

So reducing timing and adjusting idle mixture makes it hold highway speed better?.

What shape are the mechanical advance weights and springs in? Are they the stock ones? The midrange torque really wakes up when you let that timing come in faster. If you're heavy on the pedal on the highway, that vacuum advance isn't doing much. Your timing will come from the mechanical advance. I'm not suggesting you put much into it, but if you find something not right in the dizzy, linkages, choke, etc. you can get like 50hp for a couple hours work.

I may take a look at them today, By the time I was done replacing and rerouting my heater lines (PO had them going to radiator and water pump), temp sending unit (was in the spot where the heater line nipple is supposed to be), and getting a base timing and idle mixture it was getting pretty late.

I think the way the carb was set up was the biggest detractor for highway speeds? I dunno, all I know is now I don't have to floor it to hit 65-70 (flat/downhill).

 

[Shawn]

Is this a 305 or 350? The 305 is a gutless turd especially at high altitude which will knock 20% off your HP. 155hp stock, and probably 125hp when you factor in elevation. Then add large tires and the aerodynamics of a brick and its going to be tough to push 70mph. Just doing a set of heads\cam would wake it up. Have you checked your compression yet?

 

[Chevman88]

Is this a 305 or 350? The 305 is a gutless turd especially at high altitude which will knock 20% off your HP. 155hp stock, and probably 125hp when you factor in elevation. Then add large tires and the aerodynamics of a brick and its going to be tough to push 70mph. Just doing a set of heads\cam would wake it up. Have you checked your compression yet?

350 - I figured it's not worth checking compression, because even if it's low, I'm replacing the motor with an LS. Heads and cam aren't going to happen with this guy, but I do plan on a cam for my LS motor though. I just planning on driving it until this motor dies, or I finish building my LS whichever comes first, and swapping the SBC out.

 

[paratrooper307]

Those things are a convoluted mess of vacuum lines, thermal vacuum switches, and so on. If those are all stripped off, running the distributor off of manifold vacuum is what you do for performance. Ported vacuum is for emissions control.

How much should it be running vs. what it will like at idle? Injection runs the SBC at around 20* at idle. You are stuck with around 8* mechanical at idle IIRC. If you need to adjust it, you can always crank if up to 20* and see how good that is...even if you can't keep it there, because mechanical advance that high will have your starter fighting ignition. I always wanted to try that, if it is possible to find a 12* can, and see if it is possible to have high/good idle timing with a carb.

Probably won't find a 12* can, but a curve kit with a vacuum advance limiter plate does the same thing and they're widely available. I ran one when I was carbed and with full manifold vacuum it would idle around 20. Nice and smooth, worked well for me.

 

[Shawn]

Even the 350 was down on the power that year. 165hp is not that great. It was more about mileage and emissions those years. In 87 it jumped to 210hp.

 

[Blue85]

Cruising at 2650RPM the torque rating of the engine is more relevant than peak HP. While true the TBI engine made 45hp more than the 1986 engine, the torque rating was only about 25-30lb/ft higher. Even with crummy heads and small cam, the low end torque of 2 350s will be similar.

 

[Shawn]

Depending on his engine, it could be 40 lb-ft of torque difference. Minus another 20% at 5000'.

 

[diesel4me]

I think the "LL4" listing is a misprint...should say 146 HP...

It's interesting to see a 4.3 V6 is darn close to a 305 in HP and torque !.

 

[Shawn]

Yeah I think that was meant to in tq. There's also the J code military diesel which is usually higher like 155 -165hp.

quote
The 6.2L diesel was ordered with regular production option codes (RPO) LH6 (C series) and LL4 (J series). Many vehicles employed by the United States' Army were powered by the 6.2L diesel, from pickups to HUMVEES. The Army version had a higher output rating of 165 horsepower and 330 lb-ft of torque, quite an increase over the production engines.

 

[Chevman88]

Just wanted to post back with an update/conclusion.

LS swap was removed from the equation for the time being, so I decided to start really going through the the engine. I replaced plugs, wires, air filter and distributor. Plugs are AC Delco R44TS, wires are autozone, and distributor is an MSD Street Fire. She runs much better now and I hit and hold 70 just fine, hahaha.

Now I just need to get everything taken care for blazer bash...

 

[Bent77]

Just wanted to post back with an update/conclusion.

LS swap was removed from the equation for the time being, so I decided to start really going through the the engine. I replaced plugs, wires, air filter and distributor. Plugs are AC Delco R44TS, wires are autozone, and distributor is an MSD Street Fire. She runs much better now and I hit and hold 70 just fine, hahaha.

Now I just need to get everything taken care for blazer bash...

Tick tock

 

[handloader90]

Carbed at this altitude I set my base at 12° like @K85 Octane said
Mid to upper 30s full in by 3k

There's no reason it shouldn't run that speed if its tuned right unless its got some major compression or cam lobe issues

12° advanced/ after TDC, right?

I'm gonna be doing timing on my engine this weekend with the new carb/intake install.

 

[Bent77]

12° advanced/ after TDC, right?

I'm gonna be doing timing on my engine this weekend with the new carb/intake install.

That’s a good start. I also always used 91 octane and not from the squishy mart