Alternate carb for a LRP 28 S3

[olds97_lss]

Well, I don't notice a discernable difference when blowing through the new tank vs the old tank. The associated primer bulb seems to restrict things a bit. I run one of those on all my rigs, so I'm guessing fuel delivery isn't the issue.

Think I'll put on the new tank, run some DA through the primer bulb and just install the 30, then perhaps throw the 28 in my buggy just to see how it reacts there with it's tank/primer bulb... eventually. I just want to run my truck when spare time allows.

 

[DerekPike]

Well, I don't notice a discernable difference when blowing through the new tank vs the old tank. The associated primer bulb seems to restrict things a bit. I run one of those on all my rigs, so I'm guessing fuel delivery isn't the issue.

Think I'll put on the new tank, run some DA through the primer bulb and just install the 30, then perhaps throw the 28 in my buggy just to see how it reacts there with it's tank/primer bulb... eventually. I just want to run my truck when spare time allows.

@olds97_lss from your post I would gather you like the primer bulbs. I thought I saw on one forum that someone said they leaked. I'm not sure how they'd leak as long as you secured them with a zip tie, but just wondering. Now for the stupid question. Does it go on the tube between your exhaust and tank, or between the tank and the carb? I ask because I usually blow through my exhaust tube to prime my engine as I haven't had much luck covering the exhaust to prime.

I can totally relate to just wanting to run when you have time. I work full time, in college, and have a 1 year old daughter. I bought the Savage 25 like a month and a half ago and it's still not running yet. I bought a CEN TR Arena Matrix about a week and a half ago, and still haven't gotten a chance to get it out. I had time the other day and then of all things my glow plug igniter was dead, I went in to charge it and it started raining. Just my luck.

I actually found this while searching. Not sure if I'd like the 2 in 1 aspect or not. But this seems to answer my previous question of the location. It goes between the tank and the carb.

http://smile.amazon.com/Qauick-Aluminum-Filter-rubber-vehicle/dp/B015GYVZHG/ref=sr_1_7?rps=1&ie=UTF8&qid=1461880425&sr=8-7&keywords=rc+fuel+filter&refinements=p_85:2470955011

 

[olds97_lss]

The primer is made by associated, and if I remember right, was on the MGT. Mine don't seem to leak. I ziptie the primer bulb to the one way valves and ziptie the fuel line to the one way valves. It goes in the fuel line to the carb. Works well for a couple things, priming and extended roof time running.

The 2-in 1's usually leak pretty bad.

I have the 30 installed now. Will start a new thread for that chronicling it's life the best I can:
https://www.rcnitrotalk.com/forum/threads/got-a-new-engine-for-my-savage-lrp-zr-30.112864/

 

[DerekPike]

Thanks, those were the ones I was looking at before I saw the 2 in 1. I figured it was like anything else 2 in 1. It worked in theory but not in reality. I'll check out your new thread.

 

[Bajhaha]

i had the same idle issues with mine i tried another carb and it still did the same thing. my engine lost compression immediately after break in. i'm thinking it some thing internally maybe not machined correctly but idk. i ordered a losi piston and sleeve set for it to rebuild it and ill give it another shot.

 

[Certified Mike]

Maybe pointing out the obvious here but you could always put some pressure on the line out of the tank to try and 'back flush' contaminants out of the filter. With a decent additive to break up the gunk, it should blow out pretty easy and you should be able to see any 'floaties' in the tank. That may help to narrow down the issues.

Also maybe good to just bypass the primer just to test it out. I have zero experience with anything but 4 stroke snowblower, 2 stroke lawnmower primers.

 

[Steamdonkey]

I wasn't sure if I should resurrect this old thread or start a new one, but I'm in a similar situation with my LRP Z.28R (sounds like a Camaro) Spec 3. I've got the low and high speed needles set pretty well I think but the midrange is too rich. On the top end it has good power and throttle response and head temps stay around 225 F. Once up to temp it will idle just fine and even after sitting still for 10-15 seconds I can punch it and it accelerates cleanly. On the other hand if I tool around at ~30% throttle for more than a few seconds it loads up and dies if I drop it to idle or it sputters and smokes heavily if I go WOT. Since there is no midrange needle to adjust I'm tempted to try a 3 needle carb if I can find one that works with this engine and doesn't cost three figures. If I have to pay more $100 for a decent carb I might just spring for a new engine. Any suggestions?

 

[ohsnap]

If your .28 has the same sized opening (15mm) as their .32, I'd try an OS carb.
I can't speak for their current offerings or whether or not that their .21 carbs have a large enough venturi diameter for your .28's needs, but I have read of people using OS carbs to replace their LRP carbs.
The carbs off an older OS .21 RG or an .21 RZ-V99B (carb part number 23818030) are both 3-needle carbs.

The carb off an Associated Pro .28 will also fit, and like those two OS carbs, has 3-needles.
I have no personal experience with these, just that a friend gave me the carcass when the con-rod decided to "break on through to the other side" and leave a gaping hole in the engine case.

I know of a guy that fit an older 3-needle Novarossi carb on his .32 and he appears happy.
I'm guessing that his came off of a .21 as every Novarossi .28 that I've examined has a 2-needle carb.
I recently received a new Nova carb, and while it too is 15mm, it has 2-needles like the aforementioned.

 

[Littlemotor]

Once you get away from the LRP carb, you’ll likely find out that you don’t need the midrange needle.

That being said; there are several worthwhile carbs that will fit. Some require milling the carb neck down, or at the very least-stacking a second o-ring beneath the carb body. Some are worth more than your entire LRP engine, others are about impossible to find as they’re no longer made, or were just highly desirable.. Others bolt right on with ZERO modification, and will set you back only $40-$50..

OS 21J
OS 22E
OS VG30 carb

Novarossi 28x

Picco (new style crankcase engines only)

Hobao .28/.30

There are more, but combined with @ohsnap ’s reply-these were the one’s I felt are worth mentioning.

The OS carbs I listed will need the neck milled down to fit the LRP .28/.30 properly. They are also worth more than your engine.

The Novarossi will be like finding hen’s teeth, as they’re long since out of business, AND were/are highly desirable. Also need to be milled down, but not as far as the OS units.

The Picco’s are usually reasonably priced, and are a direct bolt-on.

Hobao is a direct bolt-on, tune well, are sized properly for your displacement, AND are dirt cheap. Expect to pay around $40-$50.

Hope that helps ya buddy.

 

[ohsnap]

Excellent points and guidance Littlemotor.
I was focused on diameter, not throat depth as a limiting factor.
The guy who fit the Novarossi carb to his LRP mentioned "filing" about 1mm to make it fit, but I wrongly surmised what he was filing down.

The throat of the LRP carb that I looked at is approximately 10mm deep while the Nova, Novarossi and OS 20L carb throats are approximately 11mm.
Note - Some but not all OS carbs (such as the aforementioned 20L) require a "thermo insulator" to have a sufficient diameter to fit snugly in the LRP.

Steamdonkey - Like Littlemotor said, "Once you get away from the LRP carb, you’ll likely find out that you don’t need the midrange needle."

Until last year, I had been away from the hobby for over a decade, but I honestly can't ever remember needing to change a mid-range needles setting to tune an engine.
Both the Picco's and the Novarossi's that I'm running these days are equipped with 2-needle carbs.

Having said all that, given Littlemotor's information, I'm pretty sure that I'll be buying a Hobao .28/.30 carb for my LRP should the factory carb prove problematic.
I haven't noticed any issues with mine, but I only just got it broken in and running for a couple of weeks before shutting down for the winter.

 

[Steamdonkey]

You guys are an amazing wealth of knowledge. I was considering an LRP38532 but I'm not sure it will fit and it may be a case of one step forward and two steps back. I'm not a world class machinist but I do have a lathe that I can operate adequately and would not be averse to removing some material if required. Having said that, it sounds like the most attractive options (Picco & Hobao) might be a simple drop in replacement with no machining necessary.

I didn't find any good candidates for a Picco, but I was able to find this on Hobao's site- https://www.hobao-usa.com/product/e30020/
Does this look correct for my LRP Z.28R S3?

Thanks!

 

[Littlemotor]

You guys are an amazing wealth of knowledge. I was considering an LRP38532 but I'm not sure it will fit and it may be a case of one step forward and two steps back. I'm not a world class machinist but I do have a lathe that I can operate adequately and would not be averse to removing some material if required. Having said that, it sounds like the most attractive options (Picco & Hobao) might be a simple drop in replacement with no machining necessary.

I didn't find any good candidates for a Picco, but I was able to find this on Hobao's site- https://www.hobao-usa.com/product/e30020/
Does this look correct for my LRP Z.28R S3?

Thanks!

I wouldn’t replace a fussy LRP carb with ANOTHER LRP carb personally.. Just my .02.. -as for the Hobao H30 carb you linked; Yessir-that’s the one!

 

[Steamdonkey]

I wouldn’t replace a fussy LRP carb with ANOTHER LRP carb personally.. Just my .02.. -as for the Hobao H30 carb you linked; Yessir-that’s the one!

I just ordered the H30, and will let you know how it goes. Thanks!

 

[Littlemotor]

I just ordered the H30, and will let you know how it goes. Thanks!

Good deal! You should be good to go-it’s a known problem, and that carb is a solid fix. A friend of mine runs that exact carb on your exact motor, and it took care of all the BS you have been suffering through. Glad to help!

 

[Steamdonkey]

Littlemotor, did your friend have to do a bit of machining to make the Hobao H30 fit his LRP .28? The throat diameter of the LRP is 14mm and the Hobao H30 is 15mm. I'm trying to decide if I should try to return it or attempt some modifications to the engine and/or the carb to make this work.

 

[Littlemotor]

Littlemotor, did your friend have to do a bit of machining to make the Hobao H30 fit his LRP .28? The throat diameter of the LRP is 14mm and the Hobao H30 is 15mm. I'm trying to decide if I should try to return it or attempt some modifications to the engine and/or the carb to make this work.

Oh man… We screwed ya.

That thing is OLD. I blew right past you saying it was a Spec THREE.. Jesus, I feel terrible.. I haven’t heard anyone speak on a Spec 3 in 15yrs or longer, and when I saw @ohsnap (NOT throwing him under the bus) mentioned 15mm, I obviously assumed the much more current LRP Spec FOUR.. Sonofabitch.. I’m sure you COULD turn 1mm off of the Hobao, but the whole point was “inexpensive AND direct bolt-on”.. I don’t even know of any factory 14mm carbs that would be worth searching for to be honest.. I have one here for a 20+ year old Picco P3 5TR Factory Team .28 turbo head, but they were NOT good carbs without a bunch of Band-aid’s, and even then-nothing to write home about. As much as I hate to say it-chucking it up in the lathe may actually be the most feasible option IMO.. 0.5mm off the thickness of the carb housing/barrel is nothing.. Just sucks that we are here over my goof on reading comprehension.

 

[Steamdonkey]

Oh man… We screwed ya.

That thing is OLD. I blew right past you saying it was a Spec THREE.. Jesus, I feel terrible.. I haven’t heard anyone speak on a Spec 3 in 15yrs or longer, and when I saw @ohsnap (NOT throwing him under the bus) mentioned 15mm, I obviously assumed the much more current LRP Spec FOUR.. Sonofabitch.. I’m sure you COULD turn 1mm off of the Hobao, but the whole point was “inexpensive AND direct bolt-on”.. I don’t even know of any factory 14mm carbs that would be worth searching for to be honest.. I have one here for a 20+ year old Picco P3 5TR Factory Team .28 turbo head, but they were NOT good carbs without a bunch of Band-aid’s, and even then-nothing to write home about. As much as I hate to say it-chucking it up in the lathe may actually be the most feasible option IMO.. 0.5mm off the thickness of the carb housing/barrel is nothing.. Just sucks that we are here over my goof on reading comprehension.

No worries Littlemotor. I have no doubt you provided the carb recommendation in good faith. I overlooked ohsnap's mention of the 15mm throat diameter and did not check my LRP before ordering. Considering the availability of 14mm carbs, I probably would have made the purchase anyway with the understanding that I'd need to turn it down on my lathe. If I can strip the carb down far enough it should be a piece of cake. Even if I have to keep it fully assembled, I can probably make it work with a 4-jaw chuck.

One thing that confused me about this carb is the 7mm inlet venturi / restrictor. I was under the impression 7mm was only used for short tracks or where traction was limited, but maybe they're needed for optimal tuning? I was running a 9mm on my LRP and it will fit the H30 if I can find slightly thicker o-rings. My LRP came with an 8mm inlet as well, so theoretically I could use that. What do most people run for general purpose bashing?

 

[Littlemotor]

No worries Littlemotor. I have no doubt you provided the carb recommendation in good faith. I overlooked ohsnap's mention of the 15mm throat diameter and did not check my LRP before ordering. Considering the availability of 14mm carbs, I probably would have made the purchase anyway with the understanding that I'd need to turn it down on my lathe. If I can strip the carb down far enough it should be a piece of cake. Even if I have to keep it fully assembled, I can probably make it work with a 4-jaw chuck.

One thing that confused me about this carb is the 7mm inlet venturi / restrictor. I was under the impression 7mm was only used for short tracks or where traction was limited, but maybe they're needed for optimal tuning? I was running a 9mm on my LRP and it will fit the H30 if I can find slightly thicker o-rings. My LRP came with an 8mm inlet as well, so theoretically I could use that. What do most people run for general purpose bashing?

Thanks for being understanding, I genuinely feel awful for missing that in your post. I haaaaaate giving bad information, or recommendations, and do my best not to do so-I just dropped the damned ball this time for sure.

Yep-I agree with the 14 vs 15mm conundrum/solution, and it’s tremendous you’ve got a lathe on hand. As for the Venturi; GENERALLY, the larger the Venturi; the bigger your tuning window. And obviously the bigger the power. Needle sizes may vary between carbs, so it’s not always black & white-so much as it’s a “gray area”. What’s nice is that because they interchange-you can test, and determine which your combo prefers.

Thanks again for being cool about this, and I do apologize sincerely none the less. Do keep us posted, and we like piktars around here as you’ve seen already!

 

[Steamdonkey]

Thanks for being understanding, I genuinely feel awful for missing that in your post. I haaaaaate giving bad information, or recommendations, and do my best not to do so-I just dropped the damned ball this time for sure.

Yep-I agree with the 14 vs 15mm conundrum/solution, and it’s tremendous you’ve got a lathe on hand. As for the Venturi; GENERALLY, the larger the Venturi; the bigger your tuning window. And obviously the bigger the power. Needle sizes may vary between carbs, so it’s not always black & white-so much as it’s a “gray area”. What’s nice is that because they interchange-you can test, and determine which your combo prefers.

Thanks again for being cool about this, and I do apologize sincerely none the less. Do keep us posted, and we like piktars around here as you’ve seen already!

Please don't beat yourself up over this. It was a simple oversight and with a dinosaur of an engine like this I very likely had some kind of modding in my future regardless of what I purchased. It's cool, I promise.

 

[Steamdonkey]

I was able to turn down the neck on this carb and somewhere between 14.02mm and 13.98mm I broke through the steel outer shell and exposed a little plastic. I'm able to get a thin o-ring in the remaining grove in the neck but it seems to get torn up a bit as I push it into the engine. It seems like a recipe for air leaks. Is some kind of sealant recommended in this case?