Carb and Emissions modifications

[Redneckbuddy]

Heeeey! I got a '85 Nissan 720 Kingquad. I've been fighting with that truck ever since I got it. It is the most picky truck I've ever had but I am enjoying it very much. Idle would come and go, vacuum hoses would be confused, and more. I've never seen so many vacuum hoses, even! I would like to pick your brains and experience to see if it is worth swapping the carb with a Weber and strip or bypass all the emissions but keep it clean enough to use. The truck won't climb hills well without wimping out, etc. This sort of project is totally new to me, so I would greatly appreciate your input.

[datzenmike]

This is a carbureted engine so it runs differently than the EFI you're used to. To start step on the gas and release, start. Engine should idle fast till warmed up then drops to normal.

 

You don't need a Weber to go around the emissions systems. They can simply be defeated. Most often previous owners have messed or unplugged things. All you need is the vacuum line from the carburetor directly to the distributor. 

 

What does wimpy going up hill mean? The Z24 isn't a power house on a good day. If it cuts out or jerks forward and back like it's running out of gas this is usually a dirty fuel filter between the tank and the electrical pump.

[powderfinger]

Another thing is looking at what size tires are currently on the truck. I believe factory size is 215/75/15. If they are much taller it will really affect the power. A lot of people end up putting taller tires on these trucks because it makes them look better and quickly end up regretting that decision. Regardless as Mike said, even with the factory tires these trucks don't have a lot of power.

[datzenmike]

215/75/15 is the 4x4 tire/rim size. (I don't know what truck you have) 195/205 75R14s are for 2wd. The 4x4 can handle the slightly taller tire because of the lower geared differential.

 

They have gobs of torque at low speeds but much less so at highway speeds. The next generation of engines had 50% more power.

[NoClueNewGuy720]

Is it worth it to swap to next gen engine? Thank you

[datzenmike]

Power and fuel efficiency are better with an EFI engine but a lot of bother and expense to swap and if you can't do it even more. The 720 was the last carbureted engine although there was a throttle body EFI option from April '85 on..

[Stoffregen Motorsports]

CA emissions? If you modify anything, it won't pass, unless the mod comes with a CARB EO exemption.

 

If you engine swap it, you'll need to have it certified by the BAR referee. I do this once or twice a year and it's a scary nightmare, because the rules are constantly changing.

[Thomas Perkins]

I have been using 235-75-15 tires on my 85 Nissan 4x4 .2.4 5-speed for 29 years.When I bought it in 1994,that's what was on it.My Silver Bullet will fly.31's will scrub and dig into the tires,Back in 2000,I found some brand new 31's with Toyota stock rims for sale in the News paper for 425 bucks.The guy had a brand new Toyota and was putting different rims on them.I put them on and that was a big mistake.I drove to a tire store and traded them in for some BF Goodrich and have been using that brand ever since.The 235-75-15 fit them rims.I sold the tires and rims a few years ago and now I have Black American Racing rims with BF Goodrich All Terrain tires.When they aligned the front it,it is so perfect, the steering wheel will is perfectly straight.It was 69 bucks to do that.They wear even.So in my book.235-75-15 are perfect for 85 4x4's with no lift kit.My 720 will go.I had new ball joints put on and new front rubber boots.I have no lift kit.Don't want one.Here are 2 pictures of my 720 with 2 different types of rims.What truck looks better.The one with the black rims has new paint and new lights.

Edited May 26, 2023 by Thomas Perkins

[Redneckbuddy]

You all are awesome and explained things very thoughtfully. I love this Nissan and boy, it can go through EVERYTHING and anything. I even went mudding in it after an extreme snow melt in northwestern Colorado.

 

I landed this truck for free because it sat for 13 years on a farmland and it only had maybe 25k miles on the Z24. I learned a lot from this truck and it is definitely one of the best built ones that I've seen, in spite of having a weak engine. It also is teaching me patience, too... Ha!  Yep, the Z24... Ayy. When I try going up hills on it, it falters and wimps out big time. It goes from maybe 35 all the way down to 10. Thankfully, I do NOT live in the city and I'd be run off the road and shot due to road rage. The Nissan did not do this to me before... So, I will def take the vacuum hose from the carb directly to the distributor cap and will see what happens. I can't seem to find a way to attach the before and after pictures to this forum that ain't in an URL forum... drat.

 

I do not think I want to engine swap. It's more work than I'd want to put into it, especially at this time.

 

The tires are the standard factory size at 235/75/R15.

 

MANY thanks.

 

[datzenmike]

235/75R15s are too tall. They may fit but are almost 29" tall. Stock 2wd are 195/205 75R14 and are under 26". 4x4 are 215/75R15 and under 28". 

 

Larger than stock will slow your acceleration and your speedometer will read too slow.

[Thomas Perkins]

Tires is not causing your problem.Can you put a Weber on it.

Edited June 2, 2023 by Thomas Perkins

[datzenmike]

The tires will work... just not the best. If you have a 3.889 differential then going from a 26" tire to a 29" tire makes the 3.889 feel like a 3.48 ratio and that make a lot of work for the engine to turn. The 720 was geared for economy. You shouldn't have any problem climbing hills and grades. Well, may require a down shift, but not like you describe. The Z24 has good torque

[Redneckbuddy]

After finishing a lot of my work at camps with youth and allllll that, I was able to get back to the Nissan. I went ahead and got the Weber carburetor and threw it on the Nissan, stripped off the emissions (It is not required in my area) and that solved pretty much all of the issues that I have been having. The idle is not wonky anymore, and it is now holding its speed on hills, too. I wanted to thank you all for your comments and advice. I appreciate it all. I am not a full fledged mechanic sort, but I am learning so much as I am going along by getting it done on my own along with all of your advice. Now it's time to kick work to the curb and go off roading!!